Tip #1 Dont move in bushes. The terrain in BC2 is such that anything that moves in bush is easily identifiable since the color of ghille suit is pretty different that the flora.
Tip #2 If you have been shot but not yet dead, quickly do a 360 degree turn, you WILL find a white strafing line of freshly shot bullet, take cover and shoot the bastard.
Tip #3 Another way to find from where you are getting shot is the blood stain on the screen, look out for those blood stains on your HUD, for eg, if you are getting shot from the right, you will find a red arch forming, take cover and shoot the bastard again.