So I'm just gonna go out on a limb with this and say that you haven't reached level 20 mastery on this, if you have it makes it a bit easier I guess but this method isn't exactly the hardest thing ever anyway.
To sum up this method, basically you just gotta push Dalia Margolis directly on top of Novikov and killing them both at the same time. It's probably the easiest method I can think of, and it also unlocks some other challenge I can't really remember the name of but it doesn't really matter.
If you have reached level 20 matery already, it doesn't really matter since start points don't really matter too much in this one and it might be faster without them anyway. The best starting position I can think of is starting in the IAGO auction but you'd have to leave, go downstairs, then go to the first floor for an invitation and then just go back upstairs again.

You don't need anything. In fact, I'd say it's a disadvantage to bring items, or at least non-concealable ones like guns, since you'll have to be frisked.

This is pretty easy to start out with, walk into the building, take a right, and head into the first bathroom on the right side of the hall, and pick up the IAGO invitation on the counter, its possible to get into the auction without an invitation, but it requires sneaking and a possibility of getting caught so it's better to do it this way.
After you got the invitation head back to the huge staircase, walk to the left of it, and head downstairs through the door on the stairs, which apparently no one cares if you walk through. If you get here fast enough there's a stylist that walks in the hallway, if he's there just sneak behind him or knock him out and move on. Walk through the dressing room and past the cafeteria (no one ever looks in the direction of the hallway, so you can just walk), take a left through one of the wine areas, and to the left there's the kitchen. Make sure no one's looking at the door next to the fire extinguisher and run through it, just run up the stairs and there should be a technician, you can knock him out, I'm not really sure if he can see you run past him, I just knock him out since no one will notice, there's also no reason to hide the body since no one walks past there anyway. After this guy, turn left into the area above the stage. This part's a bit tricky, you need to steal the fireworks remote off the table where the tech crew guy and the guard are talking. Wait until they finish their conversation and the guard walks off, and take the remote from behind the tech crew. There's also a patrol of two guards who walk in circles around the upper area, so make sure they can't see you during all of this.

Now here comes the good part, backtrack the way you came and go the stage area, go to the party area to the right of it, and then outside. Walk on over to the right and there's two CICADA bodyguards in front of a doorway, walk up to them and show them your invite, then just walk up the staircase and to the second staircase in the room, where you'll have to be frisked. This shouldn't really matter since there was no reason to bring anything anyway. Well hey, you're in the auction, now walk on over the auction area and press the fireworks remote. An absolute assload of fireworks will shoot off and Novikov will walk just below the balcony, and eventually Margolis will walk on over to the balcony, wait for her to lean on the balcony and then immediately push her off (no one will notice somehow). If you did it right a little cinematic like thing should play where Margolis just ♥♥♥♥♥♥♥ splats right on top of Novikovs head and they both ♥♥♥♥♥♥♥ die. Just walk out of the auction and leave the map. Easy as that.

edit 12/30/17: Turns out that it actually is possible to get caught while pushing Margolis over the side, by the guy running the auction in the back, I'll look into a more permanent and reliable way to avoid this, but chances are it just has to do with timing. I would recommend saving before launching off the fireworks and trying to time it at a point where the auctioneer won't be looking in your direction.

SO = You can do it with only your suit

A classic. The best way to do this is to bring along a lethal poison vial (has to be unlocked), or emetic poison if you don't have the lethal poison (some can be found in the kitchen) and disguise yourself as a Palace Staff member, which isn't too hard. When you start off go into the front entrance and turn left, walk down into the dressing room and take the clothes on the bench. Now that you have the disguise, walk into the kitchen area and on a crate there's a cocktail recipe, read it and head up to the bar. Head on over the left side of the bar and then make a cocktail, then poison it. Just wait a bit at the bar, then Novikov should drink it and then die.
If you used emetic poison, Novikov will walk into a bathroom, just drown him in there.

Another really easy method, outside the party area, near the stairs there's a puddle with a plug in it. To get a screwdriver, past the bathrooms, and into what I think is a souvenir shop. On the counter behind the woman on the phone there's a screwdriver. Now that you have one walk over to the puddle and expose the plug, as long as you're not doing it right as Novikov is walking towards you then no one will notice. You can be there to see him die but it doesn't really matter.

This one's a bit lengthy but I enjoy it. You have to get a CICADA bodyguard disguise. There's probably better ways to get one, but the main way I do it is turning off the generator next to the shed where the three guards are talking in the helicopter area. One of the security should walk over to it, knock him off and throw something at the guard standing in front of the shed and quickly drag their bodies in the shed quickly. After a little bit a CICADA guard should walk by and knock him out, take his clothes and put his body in the shed too. Once you get the disguise walk on over the outdoor party area and look for the man in the brown trenchcoast in the corner named Max Decker. Talk to him, and escort him to the gazebo, opposite to the area with the shed. Wait for Novikov to arrive and then start the meting up, Novikov's guard can see through your disguise but there's an area you can blend in on the gazebo. After the meeting, Novikov will tell his guard to leave and will sit alone leaning against a railing. Just push him off and you're done.

Poisning Dalia is pretty easy, first you need to get into the auction. Also be sure to bring some poison with you for this, or just steal some emetic poison from the kitchen. When you walk into the main entrance, turn right and into the two bathrooms across from the storage room. In the first one there's an IAGO invitation on the counter. Now that you have this walk over to the CICADA guards at the door to the left (if you're just walking out of it) of the party area. Now just walk up the first flight of stairs. Once you're up there, turn right into the double doors and sneak behind the Auction Staff guy and close the door behind him, then subdue and hide his body in the closet, and take his clothes. If you walk up the stairs into the auction you'll be frisked, so get rid of any weapons you might have right here. Once you're upstairs, head onto the balcony where a lot of guests are drinking at tables, walk over to the large red table and pour poison into the wine glass in the front. If you use lethal poison, Dalia will obviously just die on the spot, however it might be a bit tricky if you used emetic poison, since the bathroom she uses is off limits. If you did this, go in to the attic and vault over one of the open windows, and crawl into the bathroom through the window, and drown her.

A pretty easy one. The Sheikh's room is the room one the second floor to the right of the main staircase. The door is locked, so I'd bring a lockpick, breach charge or grab a crowbar somewhere to get in. Once you're in, go into this bathroom, and overflow the sink, eventually he'll notice this and come turn it off, once he's in knock him out and take his clothes. The Sheikh's disguise is a good disguise too, it allows complete access to almost the entire map, and you don't need any invite to get into the auction. Once you're in, sit at the chair and place a bet when the prompt comes up, and Dalia will call you in for a private meeting. The rest is pretty self-explanatory.

This could've gone under the poison category, since it is how you kill her but whatever. To get the Helmut disguise you have to go the helicopter area, and Helmut should be taking photos, wait for him to take a call and move to the back area, and knock him out when you can. You can just drag his body in the garden if the box is too risky. Take his phone, call Dalia and get your makeup on in the makeup room, and walk the runway. After this head on up to the auction (no invite needed) and talk to her. She'll lead you to a room where the guards will leave. Listen to her talk for a bit and wait till she takes call. She leaves a bottle of cyanide on the table, just take it and pour it in the wine glass on table in the room, sit back down and wait.

Sapienza SA guide
Marrakesh SA guide