i usually excel in the healer/support role where i focus my time on keeping allies alive through heal guns, medpacks, shields, turrets, etc. i try to hook up with the good people on my team and stand behind them while they dish out the damage.
i'm playing a game now called super monday night combat, it's free to play from steam. i enjoy it a lot, it has borrowed heavily from Team Fortress 2, but has also added an entire meta-game with a skill tree, leveling system, spendable in-game credits for performing various feats (multi-kill, assists, destroy turrets). At first, it was rough because i was playing it like a standard FPS and going in rambo style. that did not work out well, so now I treat it like the class-based shooter that it is and play a more team-oriented style. it's super fun. anybody who likes multiplayer PC shooters, with upgradeable, customizable characters should try it out. i've put about 200 hours into it, and only spent $3.50 total.