Most Helpful Girl
If you loved her, then nothing in the world is going to make you feel better.
If you didn't love her, then you have lots of options. Basically, do something to take your mind of it. Call a friend who can make you laugh (not a girl, because you're in rebound mode, my friend), hang out with people who can get you to stop thinking about her. That's really all you can do if you truly, genuinely cared about her. No matter what you do, there's going to be that heart-sunk, stomach-twisted feeling in your gut for quite a while (if you truly loved/cared about her) and it's going to linger, even in the back of your mind, no matter what you do.
The only thing that will make it subside is time.