For any athlete, I would strongly recommend reading the book I Dare You! by William Danforth. The book is not only a good motivational tool for athletes, but it is also a great motivational tool for life.
The whole book is based around this "I Dare You" concept, and Danforth is trying to push the reader to do things. Here is one of my favorite passages:
“I dare you to think bigger, to act bigger, and to be bigger. I dare you to think creatively. I dare you to lead and inspire others. I dare you to build character. I dare you to share. And I promise you a richer and more exciting life if you do!”
He really makes you think about things outside of sports, and it really motivates you to take control of the little things, and to take control of your life. Danforth says that he wants the readers to be "my own self, at my very best, all the time." Just reading about how simple it can be to make changes in your life that will impact society, and how much you can help others really makes you put things in perspective.
I would recommend this book not only to athletes, but to anyone. It gives a great outlook on life. Sports are typically just as much mental as they are physical, and if you go into competition with the right mental mindset then you are already one step ahead of the competition. If you go in with the wrong mental mindset, then you have already started to beat yourself. Clearing your head, and thinking of the simplicity of things can really help you when you are about to enter a tough competition.