Dr Wenger says that to develop skills in music or any other physical skill then use the Borrowed Genius. He recommends doing the BG exersise followed by actually trying the skill you want to produce, then do more BG, then 5-10 minutes of more physical activity on the instrument. After about 90 minutes of doing this something inside you just flips over towards mastery. I've tried this with martial arts training with great success.
