3F = Uppermost floor
1F = Lowest floor
Images are ordered going descending from 3F to 1F.
Every tag and item is labelled on the map.
3F

2F

To get into 3-A you first have to pick up the "Unknown Key" from the west staircase leading from 2F to 3F.
I've seen some guides that say Asuka Kato (Classroom 5-A) doesn't spawn if you explore the third floor before exploring the first floor. Sasha Shinonome (3F Main Building - East Hall) also seems to follow the same conditions.
Every puddle location is also labelled in the infirmary during the ghost event.
1F

All victim's memoirs are labelled 1 through to 5 in the order they spawn in. To make the next one spawn you have to pick up the previous one.
The only event that forces you to continue is the shadow chase after you interact with the bed in the infirmary. You can access all areas before then.