Joining oDesk is your first step in becoming a freelancer
Mostly you should already have skills in your choosen profession and an extensive work history.
Try and specialize in something as you will get paid more.
Try and build a unique profile that stands out from the rest.
Remember that almost everyone on this site claims to be an expert.
Join many websites and build a solid reputation on all of them and the work will flow in.
All this does not happen overnight.