How can I be a good UI/UX design client?

I have purchased design services many times in the past and have never had a good experience. The only time I worked with designers I liked were extremely high end professionals with $150k+ salaries in SF. But I refuse to believe that only design services at the very very top are worth purchasing. I have to assume that there is something I can do better as a client to help the process reach a satisfactory result.

Anyone have any tips on how to be a better design client?