How to Choose a PhD Dissertation Committee
When I was putting together my dissertation committee last year, I had a little chat with my department secretary. While she was shuffling paper, I gently broached the subject of how I should choose a committee and an advisor, and what I should do to make sure I made good choices. She was very helpful, but one piece of advice really stuck with me. "You run the show!," she told me and encouraged me to pick, organize, and -- if necessary -- re-organize my committee to suit my needs.
There are two biggies you should keep in mind when considering how to put together your committee. First, you want to choose committee members based on their expertise in a relevant subject. This one is pretty obvious but I think it's important. Don't pick someone who doesn't know your subject well because a) they won't be able to offer you much help or make relevant recommendations and b) the recommendations they do make might be odd or only vaguely related.
At the end of the day, you're better off approaching a professor who is a good fit for your subject, even if you don't know him/her quite as well. Sharing a common background and theoretical perspective will make things much smoother down the road.
Second, you want to choose committee members based on their working style and whether or not it's compatible to yours. This is not always something that's evident until you actually start working with them. It's nice if you've taken a course with the professor in question so that you have some idea of what their expectations are, if they're easy-going or demanding, responsive or difficult to get a hold of, encouraging or overly critical.
You might find that once you start working your committee isn't working out as well as you'd hoped. This is an issue I ran into with one of my committee members. I ended up replacing this professor, but made sure to ask around the office about the etiquette for doing this. Some departments are fine with it (remember, "you run the show!") but in others it may be a political nightmare.