The hardest thing to do and the quickest way to get her back are one in the same.

Be moderately nice to her when you see her, but for the most part go about your life as it normally would be. Date other chicks (preferably hotter than her or that put out and everyone knows it), go to parties, etc. Let her know that you are having a great time without her and she'll be jealous of your happiness. However, if you want her back, be sure to be slightly nice to her and not make it seem like you're putting all that in her face.