What is the best way to play Black ops?

Black ops has been making me mad lately,I can never kill a guy,never do anything right.It seems like when I shoot a guy first,he still suceeds in killing me.I seriously don't know in the hell what gun is best to use,I mostly use the AUG,Ak47,Galil,Famas,Commando and G11 I just don't know what gun fits my style,the G11 is probably the best gun that I am good with.Also,I seriously don't know what perks to use.Last and no least,I don't know what Camera sensitivity to play on I usally play on a 2-5.I mostly just fail at Black ops can I please get some tips to play this game?Thanks :D.