A group of advisers is one of the most valuable assets an entrepreneur can have. They bring experience, skills, contacts. First, recognize the difference between an advisory committee and a board of directors. A board of directors is a legal entity, with legal responsibilities and liabilities. An advisory committee, on the other hand, is informal.
Advisers have no legal authority and assume no liability.
First of all, people you respect. The point of advisers is to give advice. So look for people with good judgment, experience and wisdom. Ideally, of course, you'll find wise folks who are also seasoned entrepreneurs or from your industry. I'd be very wary of asking potential customers, employees, or, naturally, competitors.