Build a mental picture of the field so you know where you will be aiming your marker (to be effective, you must had already learned to shoot accurately at all ranges).
Bring your gun up behind the bunker so you don't have to waste precious milliseconds raising it when you are exposed to enemy fire.
Pop out of the bunker, pound the area quickly and pop back in, do not fallow your rounds to the target or you will get eliminated quickly
Here's the scoop...
If I want to move from one bunker to another I will crough with me opposite leg (opposite of the shooint arm; if I'm shooting lefty, my right leg is in) ready to push myself out of the bunker after suppressing the other guy. In most cases, because of the stability of crouching, I find this better because it allows me mobility but more stability.
Kneeling also can work.
I like to stay tight but I play front usually; back players usually play off the bunker to get better angles, but front players really need to stay tight to the bunker or another player might get an angle on them.
And just a quick note...practice shooting a lot. You should be good enough to be able to hip shoot at a target from about 15m away +/- some. You must immediatly be able to see and aquire a target and then put rounds on it. This isn't surgical precision, out is out!