Alright here are some helpful tips:

If you are duking it out with someone and they decide to jump out window or leave, you don't go after them(common sense,alot of people expect that).
Best thing to do is go the way hes coming from, charge at him unexxpectadley.

Another thing to do : This is common sense. If you see someone in a room, throw a nade into his only exit and then throw one in the room he's in. As he runs for the exit, the nade explodes (whip gun out shortly after the 2nd nade throw incase he jumps out the window.)

sigh, sorry for the long post, I'll be posting more.
Oh yah and first post YAYAYAYAY!

Id like to add to this if you dont mind sniper that you must always get used to the level because then you can know all the possible ways the one might come from or the quikest way to get to the other teams spawn point !!