Anyone who has ever taken any type of cardio/fitness/dancing class knows that the music can make or break the class. I try to keep that in mind in choosing the songs that I use and choreograph. I'm really hard to motivate to work out. So, if it doesn't move me, I know it's not going to do much for my dancers. I also know that I have a very unique taste in music (hello, Showtunes) so I try to keep that as under control as possible.
My advice for picking music? Variety is the spice of life. Try to add at least one thing that is unique to you. This is a great chance to pull in your background and put your stamp on something that is truly you. Try to add at least one song that's on the radio right now. When your dancers are in the car, and it comes on, they'll think of you. Much like a craving for your favorite food, your dancers will be excited to come back and dance to that song.
After your first month of teaching, try adding at least 1 new song each week. If you've been teaching for a while, feel free to pull from old choreography. Dancers that have been with you for a long time love when you pull out an old favorite.
Some things unique to the way I run the music in my classes (not recommendations, just things I do):
♫ Music. Never. Stops. I think this is the Zumba method that they teach you when you go to the Instructor Training. However, I've rarely seen it done out in the real world. Once I start my iPod/CD, I walk away from it until the class is over. I already have it formulated for alternating high and low intensities, and it makes sure to evenly distribute songs with the same style.
♫ Similarly, I don't include water breaks. I beg my dancers to get water whenever they need. Water is extremely important. I just think that my choreography is repetitive enough (without being boring) that you can step out for a minute, throw back some cold water, and hop back in without feeling like you've missed anything.
♫ No two classes have the exact same song list or lineup. I teach 3-5 classes a week. I rearrange my playlist the night before every class. Adding and subtracting songs based on my dancers, and what I'm feeling at the time. On Thursday evenings, I teach two classes back-to-back at the same studio. I've never had a dancer stay for both classes, but I still have different lists. It keeps it refreshing.
Finally, keep your game face on when you make a mistake. Nobody memorizes all of their music. It changes too often. I even change some choreography for my songs between classes, if I find myself particularly inspired by a section of the song. You're going to make mistakes. The big thing is to not let it show.
People who are good with music, or that know your routines, will know. That's cool. It's not like they're going to laugh out loud and point at you. That's not a large fraction of your class, anyway. If you can keep a cool face, continue with whatever dance move you mistakenly made, and fashion the rest of your song to make it work, then most people won't notice. However, if you say "Oh, crap" and start doing something else, people start to keep a mental tally. Do that 3-4 times in an hour, and someone will walk outside and make some comment about how you don't even know your music.
I'm no expert. I haven't even been teaching Zumba for long. These are just things that I've recognized from years of going to many different Zumba instructors in different locations, along with my background in salsa and ballroom and dance classes in general.