First, game is not fast paced like COD and clones, this is a military (as much as it can be) realistic shooter. Be prepared to die often and not knowing from where the bullet came (maybe he is 10 m from you, maybe he is on the hill, 500 m from you, u don't know), so no crazy Rambo charging.
The most difficult thing will be to see the enemy, then react depending on his position and distance.
Bullets don't go straight, there is a gravity involved. Learned that the hard way.
But overall, game is good. It's not one of those ''jump in-kill all'' games so if u expect some fast kills u will have them. You'll die fast! :P
But, anyway, its pure fun online (expecialy when u commander a tank, ey Snake? :P), and its addictive. At least it is for me. And Snake! :P
Look though controls list (its huuuuuuge) and play some single training first. Don't just jump in hoping that u will figure it out though 'baptism by fire', u will just get to many bullets inside your head. On Veteran settings (on some servers) u will not have names and icons above your teammates, so u will kill them by mistake. Happened to me lots of times.
Snake jumped in front of me behind some building and got shot by me! :P It was surprise to both of us! Haha! :P