[pjungwir]

My approach has been to have one 20-hour-a-week engagement at a time, typically 1-6 months long, plus a few 10-hour-a-month long-term relationships. I think of it like filling a jar with rocks: one big one, and a few pebbles. That helps me get higher utilization (i.e. closer to billing 40 hours a week), and in freelancing consistency is a massive help to your revenue. A lot of my "rocks" are startups or post-startups. Right now one of my "pebbles" is 5-20 hours a month via an agency that specializes in PHP but subcontracts to me when they need Rails or JS MVC work. They've also sent me a couple "rocks" in the past. Perhaps if you developed a specialized skillset (maybe JS MVC?) you could also let agencies know that you're available if that is a gap in their in-house expertise.

Good luck!