As both an athlete and a coach, I believe working on your mental game is crucial to your performance on and off the bike. One of the ways the best ways to do this is through reading. Here are some books I recommend to get you started.
Coaching: The Mental Game - H.A. Dorfman
Peak: Secrets From the New Science of Expertise - Anders Ericsson and Robert Pool
Grit: The Power of Passion and Perseverance - Angela Duckworth (my personal favorite)
The Mindful Athlete: Secrets to Pure Performance - George Mumford