-- Watch something that will cheer you up, a comedy or a favourite film.
-- Call someone and have a good talk, either about how you're feeling or something completely unrelated.
-- Come online and talk to someone, play games, etc (although personally, being online can make me feel worse)
-- Go for a walk, get out of the house.
-- Make plans with friends.
-- Do something active, go for a run, go to the gym, or any kind of exercise really.
-- Read a good book.
-- Curl up with a blanket, a pet and or/soft toy, make yourself comfortable, be kind to yourself.
-- Set small goals for yourself, think of things you want to get done and try to do so. Doesn't have to be anything big, but it stops you 'wallowing' and makes you feel like you've achieved something.
Those are just a few suggestions, but there are so many things you can do. It really depends on you and what you enjoy doing. Keep trying until you find things that help you, there will be something. Maybe try taking up a new hobby or something, and focus on that for a bit. This sort of thing can be really good, but it won't necessarily solve anything and if you're feeling like this a lot, it might be worth getting some kind of help if you don't already.
Take care of yourself, and good luck!