Move cover to cover keep scanning the area,
look don't glance, Cover is your friend in this game. The game is mainly about angles so position your self so that you have a wide view whilst only showing a very small portion of your self, there are multiple paths to use in this game so always position your self accordingly, Use the lean feature it's useful. Don't camp in obvious spots. I guess your playing normal? use the minimap if skull and cross bones appearing near you and no red marker then it's a enemy with a suppressed gun.
Recon can be extremely effect, no! I'm not talking camping at the edge of the map with a sniper rifle. Use your PLD to laze targets on the ground for engineers, spot spot spot. spotting is something very few people do but it's one of the most effect tools you can give your team, lay down an TUGS near the objective and listen for the beeps even if there is no marker on the map but your TUGS is beeping then an enemy is nearby.
Squad up! Stick with your squad, If you can get a squad that communicate then you can dominate, keep chucking out med packs and resing, if your playing support lay down suppression fire keeping an enemy suppressed can turn the tide, if your an engineer repair your fellow tanks keeping amour going is very important if you're a gunner in a tank and come into battle hop out of the tank fire a rocket and then start repairing. If you squad leader tell your squad which objective to attack\defend by using the command(spot) button, you reap in more points and unlock your squad perks.
Burst fire your gun is just done by releasing the trigger after a few shots it increases your accuracy and you can mow down more enemy's in one clip then just spaying.
If you playing normal try hardcore. I play HC all the time whilst many will say it's easy mode but it isn't... no minimap, no orange triangles above your head (the most annoying thing about normal IMO), no health regen forcing to you work as a team and you reap more points by healing\repairing more.
Adept your loadouts to the battle, I'm always changing my loadout to suit the battle sometimes you don't need a repair tool but the enemy has a tank, use land mines instead.
KDR is pointless stat IMO I have an crap KDR but I'm always mid to high on the score broad..Why? Because I play the objective, give orders, help my team out by repairing amour, spotting and playing aggressively. If your going by stats use the SPM its much better IMO.
I hope that helps.
Good place to start here, the syndicate project on BF3 was very useful to me.
Edit:
Another good tip for dealing with amour is shoot them in the back, its the weakest point on any vehicle. One shot immobilizes the vehicle second shot will destroy it even if an engineer is repairing it.