When I feel depressed* I have it really hard trying to feel better again. Sometimes I can catch myself before I get sad, think happy thoughts and smile at nothing, and sometimes it works. When I'm all ready feeling down I don't want to do anything to make me feel better, so I just sit around and mope, sadly. My boyfriend is quite good at cheering me up, though!
After being sad for what I consider too long, I try to focus on the reason behind my depression, fix it and be happy again!
(*I use the term depression in a non-clinical sense. Just think it sounds better, I'm not diagnosed with depression. I hope no one is offended by me using that word.)