There are many, but a current favourite is:
The Inner Game of Tennis by Tim Gallwey.
He was so far ahead of his time, not just in sports coaching but in helping people get the very best out of themselves.
I wish I had this knowledge 25 years ago when I set out on a teaching career.
But now that I'm older, possibly wiser, and also a coach, I better understand what he was getting at. Highly recommended for self-coaching / personal development.
Amazon.com: The Inner Game of Tennis: Books: W. Timothy Gallwey