But you actually don't have to do anything special. You just have to try and don't think about anything.
In Buddhism there's a method of essentially chanting a word. You think of a random word and just repeat it in your head over and over. And that's meant to close your mind to everything else. And if your mind begins to think of something else, you're meant to repeat the word a bit faster until you focus again. The word meant to serve as a distraction for the mind as you meditate.
Good tip! I never heard about that one before.