Smiling

Next time you're feeling down try smiling. Yes, this sounds cheesy, and I know you might feel silly smiling to yourself, but it really does help your mood improve! When you stand up straight, lift your chin, walk/stand with some confidence and smile, it's difficult to stay in a bad mood.
It's almost always easier to feel sorry for yourself, but try challenging yourself the next time you're feeling down. Never let a difficult time get the best of you!