I don't...because I don't have one.

OK, OK, don't flame me, we're in between places and it'd be difficult to change things with Tricare. However, finding a doctor, I know a lot about!
First, I find out who my insurance company lets me see. Then, I ask other people who have been - that's how I picked the best doc at the base clinic. Or, well, um, I prefer a female OB/GYN. (Just a personal thing!) So I ended up with the only female, and didn't like her. When we get to Washington, I'll be asking for lots of opinions, since we'll probably have our first kid up there.
After I start going to a doc, I judge him/her by his office staff and his demeanor. My internist was gruff, but his staff was very nice to me. I could call his nurse whenever I wanted (during office hours, of course.) Any doctor that takes the time to listen to my questions gets points in my trust book. And better still is the doc who actually thinks before prescribing. One doc just gave me the birth control pills that were being pushed that month.

My second doc actually went through my symptoms and whatnot and decided on the right balance of hormones for ME.
And, if it's something major, I always go for the second opinion.