First you should probably read the manual. Just google Nobunaga Awakening manual, or I believe the launcher has link to the manual. It explains some of the basics that I would not cover here.

Castle Development:
In this game castles come with domains and facilities. Domains come with set amount of fairs and farms you can seize (fairs for money income, farms to increase troops and food income), and has building slot you can build on it.

Your substitutes will automatically seize land for you, and build buildings there. You can help them seize lands faster by ordering its development if you have extra labor, this is cheap, but you should not build on their land because that cost some money, you should only do that to replace bad buildings that they build (for example, you don't need fortress if the castle is not on front line). Make sure to develop your own daimyo domain, this does not automatically develop. Build markets in daimyo's domain (increase fair efficiency -> more money income) unless the number of fair max is less than crops, if so you can build commons instead. Don't build other building.

Castle facilities in your capital city (where your daimyo reside) need to be built yourself, the other castles can use "castle town plan." Just set all of them to auto if you don't understand what you're doing, auto is best in 99% cases. As for the main base, start with building trading towns (how many depends on the slot the castle has), make sure to reserve slots for 1 of each of these at least: irrigation canal, rice dealer, supply depot (and build in that order after you stopped building trading post). Irrigation canal should be build after like your first 2 or so trading post, especially if you play on hard difficulty with natural disaster occurence often, to mitigate those. Rice dealer is great at producing excess food that you can sell to merchants through "trade" menu, because need money. Another thing is you might want to keep 1 slot open for gun/stable building but in smaller capital you should not do this. Foundry should obviously be built if it is an option. Do not build more than 1 training ground, and only do it last. Increasing troop count without increasing crops mean it will take longer for the castle to have enough food to support the troops, and this is a bad thing.

Next we will talk about policies and conservators. There is a minimum rank requirement before people can be assigned to these (which the game states), and do keep in mind that land holder and substitutes can NOT research policy.

The first priority is to fill every land with someone if you can because lands don't get seized by itself (unless you research gunji system which will take quite some time to unlock). Of course you can leave them empty once its fully built.

This means sometimes you might want to assign someone weak if he has high station and able to manage multiple domains at once. Senior retainer for example can be given 7 lands which means they can even manage some castles by themselves. Of course this needs to be balanced, you do need some talented officers to be made castle lord and given command of troops to actually win battles, but even a low statted lord stats can be boosted if you assign adjutants (land holders) in their domain.

If rank (or officer shortage) is not an issue, assign lords with better stats, priority varies depending on castle's position, for example frontline castle should have a lord who's decent at combat. Do note that politics stat of a castle affect its income, therefore you might want to assign higher pol guys to those combat lords who have too low of pol stats. Int stats affect defense against covert action, so you don't want this to get too low either unless it's not on the frontline. And obviously lead/valor is the most important for combat.

Grouping your lords together is important in this game.

First concept is called stacking, you want a high int castle with devious 5 for example so they can highest chance of success for covert action.

Second concept is called diminishing return and covering all bases. If you have 2 "on the offensive" guys, you can either have 1 castle have lv 4 "on the offensive" (if you put both together) or 2 castles have lv 3 "on the offensive," (if you separate them) obviously the latter option is better, so you should disperse these unique traits instead of putting them in one place.

Third concept is maximizing the affinity system. Kin and liked officer give at least +2 buff to all stats of the castle, this is very good. However sometimes it is better to split friends apart if the friend has good stats, for example you want Katsuie Shibata to have his own castle even though he is good friend with Nobunaga Oda, but those low statted Odas can be put together with Nobunaga to buff his stat up. Some officers like Ittetsu Inaba seemed average at 70s or so of stats but he has so many friends and family you put all of them together suddenly he becomes great. Same goes with the Bessho daimyo for example. Wives and daughters (and untalented sons) are generally low statted and have bad trait and thus best put together with the highest statted member of the family, exception would be those with desirable traits such as gunnery and such which you might want to put on your best generals. For example Mitsuhide Akechi already has gunnery so instead of him having gunnery 4 if you put Gracia with him, you might want to give some other general gunnery. However Mitsuhide is a special case, you want his stats (especially int) as highest as possible because he is the best at submission/policy/building etc due to his hundred poems trait. This is a superseding concept which is probably uniquely his. Hideyoshi Kinoshita on the other hand doesn't really need all these extra stats and therefore many of his friends and families can be distributed somewhere else if needed.

This game's tech tree comes in the form of policies that you need to research, often it really is unclear what the policy does.

I will cover the general policies, as for unique policies (eg. way of Oda/Asakura/whatever clan name, etc) they are good when they are free (your faction comes with them) but often they are actually not worth the council slot. The problem with them is they don't come with new submissions... and these new submissions are very useful in comparison to the minuscule buff those unique policy give. Some like Saika Village Rules is kinda nice though since it's like the only way to get musket to 10 but this is overkill, really. Either way if you have them, activate level 1 and that should be it in most cases.

First let's talk about the generic policies:

System Reform:
Allows switching of lords and land holders.
Always max to 3 whenever possible for obvious reason.

System Reform II:
Allows to set defensive base.
Only need up to the second level unless you need resupply base. They are actually not needed, notice how the AI don't use them.

Postal System:
Increase daimyo dominion range.
Castles outside this range receive reduced income. You would need to create provinces outside of this range to mitigate this penalty.
This is costly, and actually not even needed. Maybe first level max. Just make provinces instead.

Gunji System:
Allows empty domains to seize land.
Very useful if you don't have enough officers. Even if you do it is still worth activating the first level for qol reason so you don't need to immediately fill newly captured castles every time.

Defense Infrastructure:
Increase castle hp and repair speed.
Just activate level 1 if you are weak daimyo. Dominant daimyo with weak neighbor doesn't even need this early game. This is actually quite cheap to level up, late game when you can afford it you can have it like up to level 4 if you want, it's not needed if you're stronger than the enemy but hey, it is useful if you lack talent.

Bodyguard Formation:
Faster level up for attendants.
Useful if you have a ton of chiefs and have difficulty promoting them. Level 1 is all you need, unless you're like Nobunaga Oda with 100 chiefs sitting around doing nothing. Minor daimyos don't actually need this and can't afford it anyway. Level 2 max if you really like this, above that cost too much.

Hotspring Therapy:
Faster troop restoration rate.
Useful, but maybe don't activate too early if you have money troubles. Lvl 1 max, the 2nd level is too expensive for it's worth.

Irrigation Maintenance:
Improve irrigation canals.
Great policy. Priority for this is quite high if you have disaster occurrence set to high. Late game lvl 2 max, beyond is overkill.

Easy Commerce:
Increase income from trading posts.
Note that this comes with an upkeep cost, so only activate if it result in net income rather than deficit. Early game this is always deficit btw. Even late game with lots of castles you will find lvl 2 is all you need and beyond will be deficit unless you have loads of trading posts. But at that point you have unlimited money and already buy all the treasures probably.

Discretionary Power Assignment:
Allows you to set other castles to build automatically without labor.
Very important policy. Activate asap once you have few castles on your control and you can afford it's cost. Only need level 1, beyond is totally not worth it. Btw, only use auto policy in 99% cases it is best (if you don't know what you're doing just set everything to auto). Just destroy the gunnery tower later when not needed and the auto ai will build something else if it is not a frontier castle anymore. Definitely don't use "attack" (training ground spam)because that needs the most amount of rebuilding.

Marine Transport:
Increase harvest. Improve the monthly gain of food in your castles, which means you can march more often.
Level 1 useful, but not high priority. Beyond cost too much.

Mining Technology:
Improve capability when attacking enemy castles.
Great if you're attacking. Up to level 2 is worth it late game.

Silver Trade:
Increase musket tactic activation rate.
Great for muskets, obviously useless if you have no musket. Level 2 is worth. Level 3 for super late game once you don't need money anymore (it's overkill, just for fun).

Standing Army:
Increase troops per training ground.
Trash policy. I do activate postal system eventually once I had loads of income, but not this. Waste of money imo. +300 is like nothing, if you're building more than 1 training ground in a castle you will have to rebuild it later. Not even all castle would have training ground build, I don't even build in capital city unless it's like Nijo Palace with huge slot, otherwise it is lowest priority building. Even then it is 1 max, and scrap it later for more supply depots.

Small Supply Unit Deployment:
Increase days of provision limit for every castle.
Very important once you have a lot of castles and need to march longer amount of time. Keep leveling up as needed. Maybe 3rd level max, beyond only you are super rich.

Temple Donation/Western Trade:
Improve blockade or storming capability and increase loyalty of conservative or progressive tenet officers.
Level 1 max. Not the highest priority due to its cost but of course always have it activated once you can afford it.

Equestrian Instruction:
Only for clans with lots of horse ranch castles and equestrian officers, basically Takeda, Uesugi. Very low priority otherwise. Most cities don't even have enough slot to properly support both of this and gun.

Gunnery Instruction:
Much better than above because guns > cavalry. Also unlike above, comes with upgrade to arrow tower, so this is no brained for clans who doesnt specialize in cavalry. Activate this if you have big capital city that can support this building. Is it worth spamming shooting gallery everywhere? Only if you use conservator that increase musket level on everyone. It is bad if you use Musket buildup. Personally I prefer musket buildup because the malus is less debilitating, musket supplier cost too much gold until the very late game, while the minus cavalry one is great... until late game where you might have some generals that is good with cavalry and they are wasted if you have that active. Either way leveling up this policy cost money which could have better use somewhere else...

These are locked policies that needs to be unlocked by appointing council members (overseer). Only put these "code" people in these slots, the cost reduction for existing policy is never worth it because the strongest effect per cost is at level 1. More different type of policies activated is better than less policy higher level due to cost.

Demesne Preservation:
This is very good, suggestion basically allows for instant replenishment of troops in few castles, so you don't have to wait. This works even when the castle army is marching, then even if you lose troops with that army and it gets destroyed, the castle will have troops from this suggestion instead of having almost no troops. Extra loyalty is always quite nice too, it basically give everyone loyalty if they are assigned which they should be except your substitutes and situational attendants. Since it affect everyone this loyalty buff is better than temple donation/western trade and thus should be prioritized over those.

Call for Scholar Monk:
What this does is it unlocks direct negotiation possibility when you capture some enemy officers and they refuse to surrender, needless to say this is very good because you could employ those who you wouldn't be able to otherwise. It does come with extra labor and extra exp which is not bad.

Preferential Merchant:
Fair Seizure suggestion allows mass seizure of fairs. Quite good early game (for example, Kicho for Oda) for rapid development. Does not proc as much as I would've liked though, so this should be replaced at midgame when other policies are more rewarding.

Town Law:
Same like above but for farm. Farm is actually more expensive to use the manual land clearance command and hence this might seem great, but at the same time you don't want everyone to be prioritizing farms because money is tight early game.

Martial Instruction:
Good suggestion that helps with battles, also increase tactic damage. Highly recommended if you have a lot of officers that does direct damage with their tactic.

Eight Formation:
I don't actually find a lot of use for this suggestion, but the passive effects help with combat so it is quite good. Pincers happens a lot if you use manual combat.

Civil Leadership:
Allows suggestion to replenish provision which is good so you can march more often. Passive is great for late game when most castles are fully developed. Always have this activated in late game.

Ninja Code:
Suggestion is situationally useful. Covert success rate up is nice but it is quite small effect and might be unnecessary in practice. Useful if you have nothing better, it does not help with economy/development or combat and therefore due to the 5 limit of these policies I leave this out when I have the others available. If you lack high int officers to do some covert you might consider this alongside covert chance increase conservators.

Naval Transport:
Situational. Useless compared to these other policies. I'd take clan unique policies over this one.

Aristocratic Honor:
Flat buff to all your units based on prestige. This is great if you can afford it and you have loads of prestige to actually get the buff. First level only max +3 though but it is still good. Suggestion allows you to reduce enemy soldier count which is of course good. Prestige is important anyway because your army is weaker if you attack someone with higher prestige, so do invest money in relation with imperial court to raise your prestige.

Now, you can only have 5 of these. If everything is available the 5 I usually choose in late game is Aristocratic Honor, Demesne Preservation, Civil Leadership, Call of Scholar Monk, and Eight Formation.

Conservator give clan wide buffs and also come with maluses, sometimes debilitatingly so, for example Death or Glory at highest level decrease everyone's loyalty by 8 which is absolutely terrible. Many of these came in 3 levels, bronze/silver/gold color, with golden ones having the highest impact (most buff but also most debuff).

Most conservators are bad, the penalties are too damaging to be used. Here I will discuss all of them below:

Bolster Troops:
Trash, you will have loads of problem with food if you have this activated.

Provision Purchase:
Can be used for late game when you don't need money anymore. It's actually not too bad and might be more helpful than musket supplier for example when it is overkill.

Industrialist Tenet:
Increase money income, less crops. Good for early game especially if you don't need the troops (usually if you have lots of talent). Oda for example can make great use of Nagahide Niwa in this position.

Agriculturalist Tenet:
The opposite of above. Quite useless. If you have too much money you can waste it on more policies after acquiring all treasures. At that point you don't need more crops/troops either.

Rapid Supply:
Terrible. Supply is always a problem. Maybe like super early game for temporary use and then replace asap.

Recruiting Operation:
More soldiers in exchange of income. Terrible.

Musket Buildup:
Amazing effect. Can be a no brainer default conservator. Armies without musket traits don't have guns anyway, unless they have castle building which they should not have (just don't forget to give gun trait to castles that has shooting ground). Obviously doesn't work if you like higher level gun policy or conservators that increase everyone's musket level.

Improved Cavalry:
Same like above.

Improved Dragoons:
Bad. Harder to ensure than the above. Maybe if you play Masamune you can consider this, only.

Storming Strategy:
Good if you never blockade... but blockade has its use and it minimize damage to castle and losses to your troops.

Blockade Strategy:
Situational like above, sometimes you do need to storm if you're running out of supplies.

Strength of Years:
I don't like this because it can be harder to keep newly acquired officers. But 3 years is quite a short time... so maybe some people like this. Could be a lot worse but there are better conservators around. Obviously the bronze version is bad, and gold one is much better in this case because the penalty is the same.

Meritocracy:
Better than above. Lower loyalty for bad officers and higher loyalty for everyone else. But you might need these bads to seize lands so...

Sink or Swim:
Simply garbage.

Domestic Priority:
Not bad for temporary use early game.

Saboteur Tenet:
If you want higher covert chance success rate... maybe temporary use. There are many better conservator than this if you want to sacrifice troop count.

Cavalry Drill/Musket Drill:
Great if you don't use the other (no officer with traits to use them).

Cavalry/Musket Supplier:
Cost too much gold. I prefer the above, or musket buildup/improved cavalry. Elite musketeer is better than this probably.

Farmland Promoter:
Trash unless you can ensure there will never be any disaster. I play on high disaster occurence so this is useless.

Farm Return Tenet:
If you like building training grounds.... and no food to support them maybe. It's bad.

Fortress Infrastructure:
Useless. Cost too much income for the effect which is already super situational.

Civilian Infrastructure:
Just upgrade canal and build canal instead of using this.

Mercantile Infrastructure:
Also terrible. Better use money income somewhere else.

Generous Compensation/Personnel Cultivator:
Better gain loyalties through other means than these.

Overwork:
If you're small and everybody is loyal to you, this has use. Actually has use early game temporarily when you really need the labor, if you have ways to manage loyalty.

Focused:
Terrible. Increase time taken, covert action already takes so long and this doesn't even guarantee success.

Free Market Promoter:
Maybe early game but the lower level ones.

Long Game:
If you really want to increase covert chance.... I'd say it's better to upgrade the ninja policy if you need covert chance.

Slow and Steady:
Days of provision is great but the ability penalty is quite big. Not worth.

Provision Stockpiler:
Food takes longer time to restore, I don't like it.

Regional Surveyor:
Again, useless, just like all the reduce disaster conservators.

Compulsory Labor:
Not worth past early game.

Militarist Tenet:
Not needed. The penalty is not big though but there are better conservators.

Bulwark Raiser:
Garbage... unless you only defend. Not going anywhere with this one.

Elite Musketeers:
Quite good actually. Better than musket supplier.

Tax Hike:
Not worth the penalty.

Death or Glory:
Just level 1/bronze if you want. Beyond is too much penalty.

Tireless Training:
Great if you don't need money anymore.

Strength in Numbers:
This is really bad. One of the worst effect due to penalty.

Trained Garrison:
Bad. Increasing max soldier is not that important.

Elite Cavalry:
Not as good as elite musketeers because guns > cavs.

Adept Governor:
Garbage just like everything that reduce unit abilities.

People Champion:
This is actually quite useful compared to the opposite, but not worth it usually.

Trade Tenet/Rice Merchant:
Increases income by percent based. When you really need the money, the benefit of this will be minuscule, when it increase your income significantly after you have high income, you don't really need the extra income and not willing to pay the penalty.

Culinary Diplomacy:
Actually useful if you lack talent. One of the more useful conservator effect because the penalty isn't that big surprisingly.