http://www.eijkhout.net/lead_follow/turn_practice.html
7.18 On Practicing Turns And Spins
Unlike teaching her to follow turns with minimalist leads, you can’t help her spin better by leading lots of them. In fact, a funny thing about spins is that after a short while, often just a few minutes and a few “good ones”, the more you practice them, the worse they get *in that practice session*. So when you notice them deteriorating, it’s time to stop. You’ll probably find that the next time you practice them, they’re a lot better.
Finally, “mental practice” helps. In a study with basketball players, where one group actually went out and practiced free throws, while the other group just visualized practicing them and doing them really well, the two groups improved by about the same amount? Doing BOTH actual practice and visualization works even better. So, in addition to really practicing, spend a few minutes each day visualizing yourself doing spins and turns really well. You’ll be surprised!