Basically, don't do anything on a spin bike that you wouldn't do on a road bike. They include:
Push ups - useless on a bike
Riding with one hand - potentially dangerous
Hovering over the saddle - hard on your back & knees
Really high cadences or really low (pushing) cadences - tough on knees
Squats - oh yeah, I was in a class where a guy did them.

Since you will co-teach, hopefully your mentor can give you some concrete suggestions. Where will you be certified? Lots of us are certified through Mad Dogg Athletics - the original spinning program.

I cue well in advance & let people know what is coming up, like a double cadence, a hill or jumps. I use music that enables people to pedal to the beat of the music most of the time. I also mix up music - country western to rap - because everybody likes different things. If you get certified through Mad Dogg, they'll send you pre-made profiles with song suggestions. Take what you like & leave the rest.

Lots of different ways to do things - when I teach 2 classes/week of basically the same people, I have an aerobic day and a strength day.

Will you be able to make up your own classes with music? Or will you follow your instructor's classes? If you can do your own, send me a PM and I will send you some class profiles that I've done to get you started.