If you are ever in a situation where you have to engage targets from within a room, a rule of thumb to remember is: avoid standing right at a window with your muzzle sticking out of it. Doing so makes you visible to anybody standing outside and that typically results in them paying your position more attention than will be healthy for you.
In general, it is better to stand away from the window and engage targets from the back of the room. Doing so helps conceal your position and makes it harder for those outside to hit you. If you have to engage targets below your line of sight you can move forward, fire, and then move back. And referring back to lesson #3, it is a good idea to displace to another room or building when possible. If you have the ability to move, it is almost always good to do so.