Taking consistent sand divots is the key to playing well from greenside bunkers. If your clubhead enters the sand in the same spot behind the ball, you'll avoid hitting shots thin or too fat.
Here's a drill that promotes good bunker shots. Draw a line in the sand (you can lay a rake or clubshaft down to create a straight impression). This line represents your ball position. Without a ball, make some practice swings trying to hit one to three inches behind the line.
You want your divots to start in the same place each time, and they should also be a consistent length and depth. An ideal divot for a typical greenside bunker shot is long and shallow—longer and shallower than most players think. The divot should start behind the line but extend well past it, as you see here.
After you practice taking divots this way, put five balls down in a line and try to enter the sand behind each ball at that spot you've been hitting. See how close you come to making the same divots you created without a ball. That's how to develop consistency in the sand.
I say to hit one to three inches behind the ball, but it depends on the sand's firmness. The harder the sand, the closer your club should get to the ball. If there's a practice bunker, I like to hit a few shots there to check the texture before going to the tee.
Tom Watson is a Golf Digest Playing Editor.