If you haven't played before, you need to play offline to get a feel for the game first. Otherwise people will rip you a new one.
BF handles a bit different than most other shooters. The action, while it can be pretty furious, is not as zip-zip-zip as others, like UT. You can actually place shots and use the sights on the guns. Newbies usually jump all over the sniper kit just for this reason.
Once you get a feel for the game, you need to start using other kits to learn their strengths. I played SpecOps for a long time when I started, with an occasional Assault. I shied away from Medic, Engineer, Anti-Tank, and especially Support. I still don't care a lot for AT (but I have learned how to use it), but Support has become my overall fave. I also play a mean Medic now.