Not all instructors are certified to teach. The acronyms IDEA, AFAA and ACSM verify that an aerobics instructor has completed exercise and aerobics courses and has passed an exam. Find out if your health club hires instructors with these credentials. Look at the flooring. Veneer flooring is least desirable, and it's hard to move around on carpeting.
Wood flooring with spring to it is best.
Be sure the surface isn't slippery since you can fall easily. Footwear is key. A dedicated aerobics participant could easily replace shoes every two or three months. A good shoe needs proper heel and mid-foot support. You need an aerobics shoe just as you would a tennis shoe or a running shoe.