You can’t go wrong with ACE Group Fitness Instructor certification. But it is what you do after (and maybe before) you get your cert that is important. Learn, learn, learn. Take as many classes taught by different instructors ever chance you get. You might not actually workout in every one of the classes (you can only work out so much), but you can observe and learn. If there is a very popular instructor in your area, go to lots of their classes and figure out why they are so popular. Be a student of fitness and you will be a great instructor.