Exercise helped me a lot. Going for walks, and trying to focus on what you're looking at rather than worrying. I take a camera with me, so I can focus outside of myself.

Do you have hobbies you enjoy? Make time for them. Schedule them.

Also, pay attention to what you're eating. If strawberry shortcake cheers you up, eat it! If, on the other hand, you find sugar makes your thoughts race, try to avoid it and see if it helps you feel better.