I would avoid sites like Upwork (aka: odesk), elance, and anything similar like the plague unless working for less than minimum wage and dealing with morons is your idea of good contract work.
I suspect the secret to contract work success lies in having really good networking skills and a Rolodex of contacts from having worked in a given industry and having a reputation as someone who delivers. If you don't have that then you would probably have better luck finding reasonable work by going to meetups or similar industry events to build a network of professional contacts. The only way I know of to do this online is to become a notable contributor to prominent open source projects and then use that to leverage paid work.
I suspect the secret to contract work success lies in having really good networking skills and a Rolodex of contacts from having worked in a given industry and having a reputation as someone who delivers. If you don't have that then you would probably have better luck finding reasonable work by going to meetups or similar industry events to build a network of professional contacts. The only way I know of to do this online is to become a notable contributor to prominent open source projects and then use that to leverage paid work.