Anway, relaxing usually cheers me up, just taking a step back from whatever I'm doing and sitting down for a minute. However, I don't usually need to be cheered up.
Honestly, whenever I need a pick-me-up I lock myself in my room and play CoD, making sure I scream at all my incompetent teammates even if I'm the one playing bad. Nothing like getting other people pissed to help make me feel good.
Being outside often stops me from being depressed.
Or just, being with people in general. Because when youre socializing, you dont have enough time for thoughts to "brew" into something depressing.