In July, I had a lot of people requesting lessons on getting out of a bunker. In my opinion, it is a much different setup than any other shot that you would have on grass. Your stance should be much wider, and this will enable you to get lower and under the golf ball. The ball position should be played forward in your stance; this will allow you to hit the sand and not the ball. The next item is the most important: your hands should be much lower at address than normal, and you should have a much flatter backswing and follow-through than normal, trying to keep your hands low the entire time. The higher and shorter you need the ball to fly, the more aggressive you need to be at the bottom of your swing. The more aggressive you are, the more the club will dig into the sand, and the higher and shorter the ball will fly.
It is still always best to just keep the ball in the grass and not hit it in the bunker to begin with!
Grip, Clip, & Pose,
Kirk Taylor, PGA