The 30-70-yard bunker shot is the most difficult shot in golf for both professionals and amateurs alike. Very few people are coordinated or talented enough to consistently pick the ball perfectly to fly the right distance and spin back towards the hole. An easier way to play the shot is like a modified greenside bunker shot.
Go up in club, slightly open the face (about 10° or so) and make a normal swing entering the sand about an inch behind the ball. You can do some gapping with your clubs similar to how you would off the fairway, so that you at least have some distances covered. This will allow you to have some kind of consistency with these shots as opposed to guessing.