I used to have a real problem with overexposing myself (that didn't sound right...
) One of the biggest improvements I found was to turn sideways if I can, so my shoulders are perpendicular to the direction I'm coming out. That way only your gun and the top of your head come out - you're not leading with your shoulder and arm before your gun is out.
a) Turn sideways if you can. Use your knees and waist to lean so if you have to drop back in a hurry you have gravity on your side. It takes longer to recover if you're sitting back on your heels and just leaning from the waist.
b) Again, turn sideways if you can. Lean forward from the waist instead of stepping out with one foot. To help keep your balance, bend your knees and stick your butt back so your weight is on your heels before you lean. This will help keep your weight centered wen you lean forward.
c) If you can't turn sideways (bunkers too small, you have to keep switching sides) make sure you have a good wide base (keep your feet wide apart). When you lean out, use your opposite leg to balance you. As you lean right, your left leg acts as the balance. If you have to get back in quick, lifting your opposite leg will help you recover more quickly. Sounds goofy but it works
d) Laydowns are tough. One of the most important things is to be able to shoot with either hand so you don't have to expose more than necessary. I usually lay on my side with my outside elbow set so I'm just inside the bunker. When I want to shoot, I roll over a bit more until I can shoot. Some people keep their knees under them, some lay flat. Depends on the bunker and what you're comfortable with.
Most important is to practice, practice, practice. Spend some time doing snapshooting drills from the different positions so you're comfortable in them. You'll find that you start doing it naturally in a game.