I don’ t have any degree in physical education, I have passion and go to all the group classes my gym offers, one thing I can’ t understand is how and where do you learn how to plan the routine for the class , how to choose the music and so on,is it really just enough to study the material the ACE or other agency gives you?
there are many organizations to choose from, and right here at this site is a great overview with many options: http://www.ideafit.com/certifications/group-fitness.
Many things that you mention in your comments will be taught there. What ultimately makes a good instructor is a passion to teach group fitness and a lot of experience. You have already taken many classes and probably know what you like and what you don’t. As Joanne says, book learning only goes so far, the rest is practice through observation, trial and error.
I wish you good luck.