Keep a Top-Ten-Negative-Thoughts Journal, and list in it the negative thoughts rattling around in your head. You may not always be aware of these thoughts or even how frequently they appear. Notice what themes they have in common, such as blaming or criticizing. Do this for at least a week, knowing that your thoughts do not define you. This practice increases the ability to observe thoughts in a more calm and neutral way, without letting them push you around.

Donald Altman in The Mindfulness Code