pick something to do...something new that you don't really have any experience w/. go out and do it. make sure its challenging enough to completely occupy your mind
Time, time, time. Sometimes it'll just take time. One of the most important things I learned is that it's okay to keep a secret bit of your heart for them, even after you've moved along and love someone else.
(And you'll eventually figure out that it wasn't meant to be.)