If you know anything about meditation or yoga this book will be familiar for you. In case to improve your golf game you need to find how to have a zen golf mindset. What is zen golf mean? Simply the way to be present, do not have an expectation, and only focus on the present moment. Does not matter if you had a bad shot and does not matter if you will have more in the future. The key is to find the perfect attitude when all of this does not matter, only the present moment. No expectation means you will be able to play free and enjoy the game. If you can create this mindset you will play always a great game, not because your game will be perfect, just because you will accept it if it is not.
Zen Golf & Zen Putting
These two books from Dr. Joe Parenth have useful tips and advice which the best way to improve your mental game.