Thinking is a natural part of life, it cannot be stopped. If you were to stop thinking, you'd be dead, and we don't want that! What we can do is become less consumed by our thoughts, or even less identified with them. We can let them go and not have them rules our life. Like clouds passing through a blue sky, our thoughts don't have to impact the mind.

One of the best things you can do to become less identified with your thoughts is to note them as they arise. Saying "thinking" when you notice that you are thinking allows you to step back from the thought, to let it pass. Another useful way way to note thoughts is to say "I acknowledge you, thought of XYZ". This welcomes the thought in, rather than pushing it away, which takes the sting out of it.

If you want to know more about keeping things steady, check out this article.