Keep busy. Do all the things you did when you were single that made you the kind of person someone wanted to be with. Even if you broke up you probably learned some new things from your former partner, make those a part of your life so you'll remember your relationship as something that enriched your life.
Realize what a b**** the person who broke up with you is, and think of all of the flaws they have. Trust me it's hard. It just personally helps me in the long run if I do this, because if I don't, seeing him with someone else would tear me apart. Find someone else who will treat you right. Haha, that is all.