Its kind of an artform, although I wouldn't call myself an artist.
Here's the process:
1. Put on something totally cray-cray
(yes, cray-cray not "crazy")
like my floral jeans!
2. Add a T-shirt with some kind of interesting graphic. I chose my Miles Davis tee because no matter what, I look semi-deep. Make sure to ask all your too-cool hipster friends to name at least one song by him. Then make fun of them when they can't.
(I keeeeed, kind of.)
3. Finish things off with your favorite over-worn accessories. New accessories will do, but I'm too broke and in my twenties to afford any.