I usually don't have much trouble with two particular shots: fairway bunkers and punch shots out from under trees. And these two shots are very similar: grip down on the club (except in the sand one should dig in the feet as much one grips down), ball back of center, steady lower body, armsy swing. The goal is ball-first contact.
But greenside bunkers have been a problem for me; I've been very inconsistent. A greenside bunker shot is an intentional fat shot--albeit a slightly fat shot. My primary error is to take too much sand with the heel digging, and I fail to get the ball out in one shot. In other words, I hit the ball TOO FAT.
But there's a fairly failsafe method for escaping greenside bunkers. On the backswing, break the cardinal rule and REALLY cup the left wrist!!! This is going to feel so goofy and wrong (because on regular shots from the tee or fairway, it would be), but used with a full swinging motion that doesn't decelerate after contacting the sand, the ball will come out high and onto the green every time! The reason is that this ensures the club face remains open through impact and that the bottom of the club (the bounce) will be used to move sand. You can hit lower shots simply by digging the feet in more to take more sand.
There's also a good tip from Shawn Clement helps me ignore the ball more and get it out more easily. Do all of the traditional setup and swing fundamentals for a greenside bunker (or a pitch shot) but then think of this one thing: Think of hitting the sand a few inches behind the ball to the target. And being exact in WHERE you enter the sand isn't so critical, so long as you hit sand first. So the goal isn't the ball; it's the sand behind the ball that must be put in the hole. This changes the focus, because that image will help splash sand toward the target and take the ball along as an added benefit.
And how to do this (sounds easy, eh)? Setup is so important for bunker shots and high pitch shots. Really exaggerate the forward ball position, open the club face, and assume a weak left hand grip.
Elements of a good greenside bunker setup: I want the club face opened (more open for a higher shot) and club positioned in the middle of my stance; but I want the ball positioned off of my left big toe (in other words, exaggerated really forward). The more forward the ball position, the less sand you'll take and the shot will be longer and higher (go to far and you'll catch it clean and take no sand). The more back the ball position, the more sand you'll take and the shorter and lower the ball will travel. I ensure my left hand grip is very weak so that I won't close the club face coming through. I also really cup or dorsiflex my left wrist on the backswing. Then, I just make a full swing with a complete turn back and then turn through. Making a full turn and normal swing IS important. Also, stay loose through this shot and feel the club head; tension will kill the shot. Done correctly, even a slow tempo will blast the sand and the ball out of the bunker towards the target.
Another way to think of the greenside bunker shot is to setup and swing as if you're hitting a driver. This means the ball is off the front foot and the swing going back and through is shallow (more around the body rather than up-and-down)--the way it needs to be to keep from taking too much sand.
A lot of these same principles will work for pitch shots as well. You can even play the ball off your big toe for pitch and flop shots and not fear hitting fat. With the weak left hand grip and opened club face, you'll usually slide the club along the grass before launching a high piercing and spinning shot.
1) Get good footing: Grind your feet firmly into the sand. This will help promote a solid stance and good balance. It's also a way of doing some detective work, to determine the texture and consistency of the sand. Since the Rules prohibit you from grounding your club in a bunker, you should try to learn as much as possible about the lie as you take your stance. 2) Choke up about an inch on the club: When you grind your feet down into the bunker, you bring your hands closer to the ball, so you need to slide them down the grip. Otherwise, you'll tend to hit well behind the ball and dig too deeply into the sand. 3) Open your stance: Most bunker shots require a steep downward attack on the ball; an open alignment, with the feet, knees, hips, and shoulders pointed well left of the target, will facilitate this type of impact. You'll need to open up various degrees for the different shots, but it's safe to say that 90 percent of bunker shots are played from the open stance. 4) Don't keep your eye on the ball: Instead, watch a spot about an inch to an inch and a half behind the ball, because that's where your impact should be. Since you don't need to hit the ball on this shot, there's no reason to look at it. Again, the precise spot will vary, but suffice it to say that the spot is never on the top of the ball.
From Learn The Basics of Sand Play by Greg Norman
Most amateurs swing the club into the sand, and when they feel the resistance, they quit on the shot. Plus, they're fearful, so they tend to lock their bodies in place and just wave at the ball with their arms. Commit to turning to a full finish, and you'll get the ball out every time.