Out of all the ways to twist and all the drills out there you could use, the following is so simple, it's ridiculous:
When pulling the body up to the arms in a layout (such that the hands end up by the thighs), have the gymnast pull both arms down on top of one thigh for twisting the layout. The opposite side hand will rest on top of the same-side hand. That's it. The gymnast does not have to try to twist. It just automatically happens. Seriously, it's this simple.
The other month, I had a level 5 on trampoline who was doing pretty decent back layouts. The coach who taught me this method of teaching twists wanted me to teach it to this kid so he could make sure I understood the technique and could teach it correctly. I explained to the gymnast what I wanted her to do, tested her arms to make sure she could pin them tightly on top of her leg (on the side she showed a natural proclivity for turn-direction). She set, flipped the layout, and pulled her arms down (really, it's pulling the body up to the arms) on top of one thigh. I slid the throw mat underneath her and she landed her first full. She asked, "What just happened?" (We didn't tell her she was going to be twisting). She then repeated it two more times. After her turn, she watched the next gymnast- an optional- do a full and asked, "Is that what I just did?!" Of course, since then, we went back to teaching her to do halves as well.
The point I want to emphasize here is that this is by far the simplest method I've ever come across on teaching back twisting. No land and jump half turn. No one-two with the arms. No spotting. No fancy drills and complicated setups. Seriously simple. I've used it a number of times on tumble trak and usually the gymnast first will land a half; but it doesn't take long for them to start turning fulls. Just make sure they have nice layouts and always go back to layouts and late halves. When adding more twists, the arms go the same way, but just curl the arms up.
