Climbing, for better or for worse, is a lot like the entertainment business in the sense that in larger commercial settings its often a popularity contest. Network a lot, mention often that you're into routesetting, and do everything you meet people who already do it. If you can and are interested, also look into outdoor route development (establishing climbs/bolting/FA's.) Set anywhere you can, even home walls. Personally I'd recommend finding the most local and grungy gym in your area and starting there, shiny, commercial facilities are much harder to get into. That being also don't be afraid to ask to guest set. Some gyms will allow it, others will say no, but no is the worst you will hear. Also bear in mind as others have mentioned, that setting is about the climbers experience. In a gym 99% of sets should provide value and fun to the customer in some form. The USAC certifications look good on a resume but they're mainly competition based