As a Man Thinketh is an amazing little book (about 41 pages) that teaches about the self mastery of ones thoughts. I think it's beautiful. Here is the address to the full text online. [link]
These are the chapter headings to help you get a picture of the book. It's a wonderful book on thinking and changing your character for the better. It was written about a hundred years ago by an English man named James Allen (1864-1912). I just want to encourage everyone to read it. It's very short and very powerful.

Thought and Character
Effect of Thought on Circumstances
Effect of Thought on Health and the Body
Thought and Purpose
The Thought-Factor in Achievement
Visions and Ideals
Serenity