I found that the key was to find clients who value your work. Working with individuals or small businesses can be tough because they are usually highly constrained by budget and do not understand everything that goes in to what you do. They want freelancers because they can't afford full time people. They will compare you to the rates they can find on Craigslist or Elance and balk when you require market rates.
Instead, find startups with technical people doing the recruiting or large companies with established roles and processes for freelancers. They will at least understand market rates and what you actually do.
You also need to have the power to say no to clients. That usually means savings and the willingness to wait long periods between jobs in order to find the right one. For me, the hit rate of was 1 out of every 8-10 job opportunities.