Something I learned from a friend a long time ago was that if you start flipping, which I had a tendency to do, focus on a spot about 2-3 inches in front of the ball (target side of the ball) instead of focusing on the ball itself. This always did the trick for me and I will even do it on the course if I start flipping or hitting shots fat.
I also bought a DST Compressor and practice with it regularly. Not a ton of balls but about 10-15 and that helps to ingrain the proper hand position. It's a curved club that forces you to put your hands in the impact position at address. If you're flipping, you'll know. Without a doubt.