I've been reading this excellent book on tennis called The Inner Game of Tennis and I think it could apply to many things and not only different sports. It's about reaching what many sports enthusiast call “the zone” through finding a term that author Timothy Galway call relaxed concentration.
So how do you reach that stage where every stroke or movement comes natural to you? A lot of the book deals with being less judgmental of yourself, you know how you want to scream “Idiot” or something even worse every time you mishit a shot or do something stupid on the court? What happens when you start belittling yourself and force yourself to improve your technique or rotate that wrist, throw the ball higher on the serve, and move your feet better is that your muscles tense up and you end up not improving at all, but getting more and more negative and starting a downward spiral which might end up with you breaking a racquet (this has happened to me at least, several times).
What you need to do instead is more of a zen approach, to look at the situation and the performance more objectively, and analyze where your racquet head is through the swing, how you're feet are moving before the shot, and if something isn't working not to scream at yourself, but to say to yourself with some distance: “Aha, I think I was hitting it a bit behind me or, I didn't come through properly on my forehand. I need to pay attention to where my feet are or how the racquet head travels through the swing.”
This kind of thinking will help your muscles and mind to stay relaxed (relaxed concentration!) and identify what is wrong in your game. If you don't know you should probably ask a coach or a tennis pro to help understand what you lack in your technique. The key is definitely to quiet your negative thoughts and to evaluate your play in a more balanced and objective way.
The Inner Game philosophy has a lot going for it and can be applied not only to tennis but to other sports and areas of life as well. I can very much recommend this and other books in the series.
Go improve your Inner Game now.