Look in your local newspaper periodically to see if a local AAU team is holding tryouts in the sport you're interested in. If they are, the tryouts will usually be posted a month or two before the beginning of the season.
Go online and visit the national AAU website. Search for a team in your chosen sport in your region and contact the coach that is listed.
Contact the parent of another athlete you know who does your AAU sport and ask how to contact the coach.
Sign your son or daughter up to try out for a team. If he or she makes the team, you will need to fill out the appropriate forms and releases and pay the necessary fees.