My impact drill: Set up to a rake and swing, bouncing the club's back edge off the handle. This bouncing action is the key to sand play.
To stop chunking your bunker shots, you must make the back edge of the clubhead enter the sand before the leading edge. Feel this with my drill. Get in a bunker and set up to a rake (above, left). Open the clubface, which puts the back edge lower than the leading edge, and swing, skimming the club off the rake.
You'll quickly sense what it feels like to hit with the back edge of the club. Now transfer that feeling to an actual shot. First, lower your body a few inches so the clubface can slide under the ball. I do this by widening my stance (others twist their feet in). Then, play the ball off your front heel, and remember to open the face.
Make a three-quarter swing, accelerating the club past your hands through impact. The back edge should enter the sand two to three inches behind the ball, which will help the clubhead slide and push the ball out. To prevent the club from digging too deep, keep your body turning to a full finish.