If you look around when you are feeling down, you will see things that confirm your mood. You may notice a person crying and not see a person laughing. To break your mood, you can practice being aware of what you see and focus your attention on pleasant sights. Look for happiness. Look for people smiling. Look for beauty in what you see.
When you find yourself stuck in a bad or sad mood, you can use your awareness to help improve your spirits. If you are aware of what you perceive around you, you will notice yourself seeing ugliness and despair. If you actively look for beauty and joy, you will jar yourself from your habitual mood. Look at the world around you and you will find what you are looking for. Look for beauty and joy and things will start looking up.