Let's face it, music rehearsals can be DRY. Here are some of my favorite music rehearsal techniques to keep them fun, fresh, and approachable.
Use the tempo of the song to set the pace for that section of your rehearsal.
Take a short break when it's time to switch and transition.
I frequently use the concept of repetition and call and response to allow kids the opportunity to learn a passage. Chunking is such a helpful tool here!
It's also important to model the way you want something to be performed (especially without a piano, or piano prowess).
Normally I always advocate for live accompaniment whenever possible, but without a music director sometimes it makes more sense to use the tools available to you. If you know you don't have anyone to play and/or coordinate and conduct live musicians, the tracks might be a good route to explore.
Rehearsal track programs offered with your show's package are worth the investment, especially without any kind of rehearsal accompaniment.
With some shows the cast recordings can also be decent resources, but be wary of edits and cuts made to allow for more seamless listening. Ask a trusted musician friend or student to look at the music and make sure you have a match before using it for any kind of rehearsal or learning exercise. The internet might have resources for this as well!
My friend Karen Nave at South Lyon High School assigns trusted student musicians to be vocal captains for her shows. Usually a low (male identifying) singer and a high (female identifying) singer. Alternatively utilizing a vocal captain per voice part can be effective in this space
Simplify! It can be very effective and easy to pair down a section or piece that is written for five part harmony into two an approachable two part experience. Chose the melody and an easy harmonic line and allow students to choose their own line in whichever octave is most comfortable for them. Most students will default to the melody, leaving your more musically inclined students to try the harmony. This will usually balance itself out really well.
Choose your own adventure; sometimes if I have a group that collectively has a set of really good musical ears, I'll have them choose their own harmony (usually on the final note of a tune), and sometimes they create a sound better than what I could have assigned.
It's important to keep in mind that they feel most successful when they know that you are their biggest fan.