Life is a mind game and Abraham Lincoln already knew it when he said:
People are just as happy as they make up their minds to be.
By controlling your mind, you control your life. In every single situation, you have the choice of how you react to it. Everything is up for interpretation. Will you react positively or negatively? Will it make you happy, angry, or sad? Will you learn from it or ignore it?
But, how do you actually achieve full control of the mind? Often, your mind just wanders along, jumps from one thought to the next, dwells on past experiences, imagines unattainable futures, or gets all emotional. How do you stop that?
By literally saying "STOP". You can do that in your head or out loud (although this might get you strange looks). Every time you catch your mind not doing what it's supposed to do, which is being calm, clear, and focused, you say "stop" and pull it back to your area of focus.
Tell your mind what you want it to focus on. For example, the nice breeze, the beautiful sunset, the project in front of you, your kid trying to show you something, your goals, lifting the barbell, or writing the 200 words.
You have full control. Use it!