Practice breathing

This is as simple as it sounds.

There are different techniques you can try, for example: inhaling counting to 4 and exhaling counting to 6. You can exhale through the mouth if you like.

Another technique is: inhaling, pausing, exhaling, pausing.

Since all you need to do these practices is breath, you can do this anytime, anywhere.

By following these techniques you focus on your breathing and this helps you clear your mind from unwanted thoughts and it also helps your nervous system relax.