BC2 was my first Battlefield game; I always played COD games more as well as Halo so I wasn't as used to the big maps and necessary teamwork.
Here's what I'd suggest:
USE THE SOCIALIZE BUTTON. I cannot stress this enough. On the Xbox 360 and PS3 it is the Back/Select button. What it does will change based on how you use it. The most useful function is spotting enemies. If you see an enemy, hit it while you're aiming at them and they will show up on everyone's radar. It's basically the Battlefield equivalent to Call of Duty's UAV. A typical player who isn't actively fighting or pursuing an enemy will always gravitate towards players that have been marked. Only caveat is to not mash it. You can use it about once every 2 seconds. If you mash it, it'll just stop working for a few seconds until you stop.
The socialize button also can indicate that you want your team to attack or defend a control point or to ask a friendly vehicle to stop and give you a ride, but it's used a lot less that way.
Learn how different weapons work. They aren't the same as COD. Grenade launchers are more useful for blowing out walls on buildings, unlike COD where you just shoot them at an enemy's feet and they die. You can't do that in BC2. But if an enemy is hiding in a building, you can blow the wall out to hurt them and expose them to fire.
Assault rifles are best fired in short bursts. Machine guns can be fired continuously without losing too much accuracy. I'm not totally sure how the recoil system works but I think bullets can travel away from where you're aiming, so you have to be careful. In COD your bullets always go where you're pointed if you're aiming down the sight, and the only inaccuracy comes from physical recoil. I am pretty sure you have a firing cone in BC2 even when aiming down the sight. Not 100% though. Regardless, weapons do less damage and have more recoil so you will usually need to be closer to get kills.
Health doesn't regen nearly as fast. Instead of getting instantly healed to 100% after five seconds, you start slowly regenerating 3 health per second after 5-6 seconds of no damage. So if you were at death's door it will take ~30 seconds to heal fully.
Make sure you use your class's abilities a lot. Note: you will not start with them but you get them after playing a bit with each class. As a medic you don't start with medpacks or paddles but you will get them. Same with assaults and ammo packs, engineers and the repair tool, or recons with motion sensors and mortar strikes. Basically, throw ammo or health at your teammates or even at your own feet as often as you can. You help yourself and everyone else. Plus it's worth lots of points, so you unlock new gear faster. It's always a good idea to follow an engineer around if you're an assault so you can restock their anti-tank weapons, or to follow anyone as a medic to replenish their health.
I have the game on PC, can any console players confirm that there is a voice localization option on the console versions? If there is you should turn it on. By default (on PC), Russian players will actually speak Russian which is kind of unhelpful if you can't understand it. Better they speak English with Russian accents so you know when your teammates (or enemies) are reloading, healing, spotting a vehicle, etc.