I found this great 3 minute video:
It that explains, in simple language and fun animation, the power of your imagination, how we learn (and can learn faster and better) and why visualisation works.
It seems that your brain loves repetition, practice really does make perfect, and mental rehearsal is a proven and powerful tool to help you become more effective in almost any endevour. The improvements are not limited to cognitive tasks but apply to performance on psycho-motor tasks too.
Additional Resources:
Ahead of the Game: How to Use Your Mind to Win in Sport
Creative Visualization: Use the Power of Your Imagination to Create What You Want in Your Life
Wishes Fulfilled: Mastering the Art of Manifesting