Step 1 – find out whether your instructors have group exercise certifications. ACE, AFAA, or ACSM.
Step 2 – Just because someone has a certification doesn’t necessarily mean that they follow it. Ask them whether they remember the safety rules and contraindications related to their certs, and how they incorporate those rules in their classes.
Step 3 – Ask them what continuing education they’ve taken within the last 2 years. Their answer might give you an idea whether they’re more interested in choreography (not necessarily safety) or exercise physiology (more likely to know and care about safety)