Technique is easy. GO SLOW AND STAY DOWN.
Take your time. Be very sure there are NO
enemies around before you so much as move
your team to even a crouch, keep a finger
on the Q (dive quickly) key when you are in
anything but a prone position, and NEVER
RUN (except possibly the last coupla meters
to the extraction vehicle.
Also, on OBSERVE missions, make sure you are
very (at least 50 meters) far (but still in
targetting range) from the objective you are
observing being destroyed. Once I was only 30
mters from the bunker the helicopters were
destroying and the idiot gunners still cut
my team to shreds.