A few basics:
Your weapon is not a lazooor so take aim, wait, and shoot.
If you jump you can't fire your weapon for about 1-2 seconds after you land, so don't bunny hop or you'll get yourself killed.
Winning depends on the coordination of your squad and your team, work together towards a common objective.
Do what your Squad Leader tells you to do.
The shovel is used for constructing assets(Firebases, foxholes, AA, HMGs, etc.), just stay next to the asset and hold down the mouse key to construct.
Keep your greasy little fingers off the vehicles and limited kits(These can be requested through your comm rose if you're next to supply crates). Vehicles are not your personal one man taxi, and choppers/planes do not operate in the same manner as in vBF2(Set up a local server or join an online training server and get good there before wasting assets on game servers). Tanks and APCs require two crewmen, one manning these assets will get you kicked from the server.
No, the squad does not need your 1337 sniporz ability, stick with basic kits or whatever limited kit your SL tells you to pick up(He might, on some occasions, tell you to pick up a marksman or sniper kit

).
SAWs(Automatic Rifleman kit) have two modes, deployed and undeployed; in deployed it will only fire when you're prone but with excellent accuracy, undeployed it will fire in any stance but with a lot less accuracy.
Sniper and Marksman kits require you to stay still for some time to settle in before you can aim with any accuracy(Find your spot, lie down, wait 8 seconds with sniper, then you can fire with great accuracy every 2-4 seconds as long as you do not move(WASD) or do a 180 degree turn).
To fly you need a pilot kit, to drive APCs, Tanks, AAVs, and so on you need a crewman kit.
The Medic has resuscitate and epipen in his inventory. The resuscitate is used to unstick players from objects and so on(Which makes them unrevivable as long as they're stuck), the epipen works just like the shock paddles. To heal with the medic bag you hold down your mouse key.
And lots of other stuff that I can't be bothered to write right now.