Gain experience. Look for local beauty pageants that may be small, but will provide you with experience. More prestigious pageants will look favorably on someone who has experience. Find pageants in local papers, community bulletins and classified ads. Apply to be a judge at those pageants.
Get involved in related industries. Beauty pageants are often sponsored by cosmetics companies, fashion designers and jewelry manufacturers. Work for a company that sponsors or is associated with beauty pageants. Use the position in the company as leverage when approaching pageant organizers about being a judge. For example, if you work for a cosmetics company, approach pageant organizers with a cross promotion idea of offering cosmetics as a prize for contestants.
Take classes to become certified. Many states offer courses to become a certified pageant judge. These classes are generally offered through the governing beauty pageant body of the state. Each state has an official "Miss NAME OF STATE" pageant that is usually run by a governing body. For example, the Miss Texas Pageant is run by the Miss Texas Organization. These courses are not free and prices vary, but most are under $1,000. Not all certification classes accept every student. Some may have an application process that requires experience or industry expertise. However, most are just happy to have the student pay the course fee. The certified pageant judge course can usually be found by contacting the organizers on their official website.
Network. Attend pageants and make friends with pageant organizers and participants. Get to know people at the pageants and ask them about the process of becoming a certified judge. Many pageants will bestow the title of "certified" on a judge who is a regular pageant judge.