How to master emotions and thoughts?

As the lord and master of your thought, you are the maker of yourself, the shaper and author of environment. 

Even at birth, the soul comes to its own, and through every step of its earthly pilgrimage, it attracts those combinations of conditions, which reveal itself, which are the reflections of its own purity and impurity, its strength and weakness.

James Allen, As a Man Thinketh, Thomas Y. Crowell, New York, 1913, Chapter Two, Effect of Thought on Circumstances, 15