I would start here and look up all the different organizations that will give you a group fitness certification. Here is a link http://www.ideafit.com/fitness-certifications. I would suggest that you look for an organization that is NCCA accredited. They have a higher standing n the industry. If you have a place in mind where you want to teach classes, you can also check with them whether they have a preference.
In addition to what Karin mentioned, I would also seek out a mentor in group fitness. Having someone who can teach you some hands-on things about cueing, monitoring the class, giving modifications, music speed, etc. It will be helpful to have someone to give you advice as well as someone who can answer questions for you.
Hello Tara Craw,
I also like ACE; but, there are many you can look into. Try taking some classes and talk to the group fitness instructor to see what they like. Different areas prefer different training organizations. IDEA also has a nice list to choose from. I would also choose the NCCA choice over someone else.
Natalie aka NAPS 2 B Fit.