Become a USAG professional member and get your safety certification. Then, buy a compulsory book, learn the routines and deductions for each individual skill for L5/6, and learn the general deductions. Levels 5/6 are the only ones tested, but you should be able to judge any routine in the book. You have to sign up for a test online (under the "Judges") section on the USAG site, and once you get your certification, you'll also need to become a member of NAWGJ.