If you're struggling from greenside bunkers, be mindful that the more you cut across the ball from out to in with a wide-open clubface, the more sidespin you impart on it. It's hard to control the starting direction of the shot, and the spin after landing is unpredictable as well. That's why I'm a proponent of a pretty square clubface and a proper swing path through impact.
At address, set your stance slightly left of the target and open the face just a little. On a standard bunker shot, make sure the path of your swing through the sand runs parallel to the line of your feet, or slightly out to in (above, right). If you swing too much across the ball (above, left), you'll make a glancing blow and won't deliver enough energy into the sand to push the ball out. A little out-to-in is all you need.
Making sure your swing bottoms out in the right spot is essential to consistent bunker play. Here's a drill to help: Draw a line in the practice bunker and address it so that it runs directly in the middle of your stance (without a ball). Make your normal bunker swing, and try to splash a divot that starts on the line and points toward the target (right). Repeat this exercise a few times to develop a feel for bottoming out your swing in a consistent place.
If your divot starts behind the line, your sternum is too far back at impact. You should start with your weight favoring your front foot and keep it there throughout the swing. Once you're good at starting the divot on the line, place a ball one inch in front of the line and repeat the drill the same way. When you learn to control your sand divot, the ball will pop out perfectly.