Practicing mentally is an important component of sports performance. It is proven in scientific studies that imagining clearly the motions and actions you take in hitting a ball can actually improve your skills as much as going out on the court and doing so. This applies to golf, archery, and any other discipline that you can practice in your mind as well as on the field or court. Of course you can't bypass physical efforts completely or even the majority of your training, but adding a considerable amount of time using mental imaging will give you fast improvements.
The original theory for this approach to self improvement is a book titled Psycho-Cybernetics by Maxwell Maltz. It is well worth reading and using the knowledge you get from it to change many aspects of your life. In addition to working for your sports performance such as how you stroke the ball you should consider also imagining yourself winning against specific types of players or even specific players. Go through the mental steps of visualizing your strategy, how you hit the ball, the movements you make, and the shots that you take. All of these aspects of your game can benefit from imagining yourself doing something as an accompaniment to your on court efforts.
Here is the book that I suggest you read to understand fully the value of this added aspect of training for mastery.
If you're not into reading a tremendous amount or don't have the time consider an audio version of the book.
