Mental imagery (visualization) in sport consists in mentally visualizing an activity. For example, I can mentally visualize a positive memory of the best game of my career. The exercise is then to close your eyes and try to relive this positive moment.
Find the optimistic viewpoint in a negative situation. Don’t make a mountain out of a molehill. Say Stop - Breathe - Refocus. Learn to take criticism in a healthy way. Don’t reply right away. Really listen to the criticism. Remember that the criticism isn’t always about you.
Learning to remain joyful throughout the day can have dramatic positive effects on physiology and even improves the overall mental function. Isn’t that enough reason to keep smiling?