accuracy/reaction time/map knowledge/battle smartz
gotta learn how to shoot, gotta react faster than your opponent, GOTTA know the maps(everything around you, camp spots, strategic spots), and you have to, have to have battlesmartz. get headphones!!! sound is very important in this game. relay what sounds you hear to what you see around you and on radar and that will tell u a whole bunch, n i cant even stress that enough! battlesmartz would be hearing that your enemy is reloading and taking action, or knowing when to kill someone, they may have friends following them right around the corner. reaction time and accuracy will come with time, but you need to always work on it. only burst, never spray, try not to move when you fire either. oh, n learn how to throw nades properly!
ps......use the shotgun, its l33t -_-