Research on mental rehearsal has encompassed dart throwing, piano playing, and many other skills, often reporting improvements in skill that surpass actual practice. Focussing in the effect of a movement works better than focussing on the movement itself, and the level of detail you can produce in your rehearsal says a lot about your actual skill level. There are a few ‘health warnings’ about ways of (perhaps inadvertantly) doing rehearsals that are not helpful.