When you are on the run from the guards after sniping Nicoladze, in the dining hall climb on a cabinet. Then, jump to the balcony that you see. Go through the door in this room. You will find four guards. Do not shoot them yet. Instead, sneak upstairs and turn off the light. Crouch in that corner and snipe them after they come up to the level that you are on. You will be able to shoot all the guards because of their curiosity to find out what is going on upstairs.

After you take the elevator down to the library and have to fight all the guards, instead of going against the guards and using up ammunition, use the following trick. When the elevator opens, run to your right and towards the flight of stairs. Run to the left of the stairs into a flight of stairs that will lead down There will be a guard there. Do not shoot him. Instead, just pass him and he will not shoot or follow you. Do not run to the door to the right of the stairs, as there are two guards coming up there.