Consult your mentor about local norms.
How are committees assembled? How are they comprised? For example, most dissertation committees must include a specialist in methodology and statistics.
Get folks your advisor likes.
When it comes to which faculty to invite to sit on your committee, seek your mentor's advice because you need someone who you mentor feels he or she can work with. Also, your mentor will have info about the professor’s personality and history as well as how the faculty you select get along. Dissertations are not just about a student completing a degree - they're about politics too. Select a faculty member who doesn't get along with your advisor and you may have a committee member who is difficult and just plain hard to work with -- and who finds fault with your work simply to get under your advisor's skin. It happens and these interactions can slow down your dissertation and keep you in grad school longer than you want or deserve to be.
Learn from other students.
Seek input from other students as to how they secured a committee, what kinds of things they looked for, and their experience with particular faculty. For example, some professors are notoriously flaky. They miss meetings, forget to read your work and run behind. They may be very nice, helpful, and easy to get along with, but they can interfere with your progress.
Trust your instincts.
Make it a point to get to know faculty throughout your grad school years. As you take classes, talk with faculty, and watch faculty interact, keep the dissertation in mind. Trust your gut. If someone seems like a terrible choice, even if he or she is a very successful professional, you should trust your gut and think twice before asking him or her to sit on your committee. This doesn't mean that you should exclude successful, but difficult, people. It simply means that you should go in with your eyes wide open.
Knowing who to choose for your committee really comes down to communication. It’s about getting to know faculty, communicating with your mentor about your needs, his or her needs, and potential candidates, and communicating with other students about their observations, experiences, and history. Also, recognize that some dissent among dissertation committee members is part of the process. Some debate and disagreement can improve your project. The goal, however, is a healthy and constructive debate.