oDesk clients tend to be one of two types: Skilled project managers/architects/agencies looking for subcontractors, or businesses looking to save a buck by not hiring the former.
The first group are great, they know exactly what they want and will pay for quality. The latter are hell as they often have no idea how to communicate requirements, scope, process, etc and want everything cheap.
If you live in the first world and have the communication skills, the best place to find freelance development work (IME) is still community networking.
Basic thing is ; don't go for mainstream. You cannot compete on price doing PHP or something like that. If you have something 'niche', you can pretty much ask what you want and get it.
There are actually quite a few excellent clients out there on those sites but they actively won't talk to people who bid at the level of the bid-on-everything-then-outsource "suppliers" who plague freelancer markets.