Getting started can be the hardest part. Nearly ALL instructors were "discovered" as participants. So, if you want to teach in a particular club, take classes there. As you become familiar with staff members and managers, you can assess which certifications are preferred there. Every facility has a "gold standard" that can vary slightly. My current position came through much experience within a particular company and an article that received a lot of attention within the industry. The best instructors typically have a degree in a health or fitness related field and are certified by ACE, AFAA, ACSM, SCW, or one of a dozen other certifying bodies. Les Mills International has some wonderful certifications as well.