Whether using a 35mm camera or something digital, the idea of photographing a live performance is for the photographer to stay on the move, just as the performers do. Set your apertures and lenses and then just start shooting. After taking a bunch of photos, you can change your lenses and settings, but don't fiddle between each photo or you might miss something amazing.
Remain respectful and unobtrusive. Don't wear shoes that make clomping noises and don't run in front of the action---ever. Use silent flashes and don't choose a camera that makes lots of noise. Yes, you are part of the artistic moment, but you are not the focus.
Get faces whenever you can. Go to rehearsals before performances and practice shooting them. Remember when a performer makes a certain gesture or facial movement and be ready to capture it.
Adjust your lighting. The performance itself has its own lighting requirements, so you can't expect your needs to be met. Get the right flashes and exposures set so that you have a visible shot even in a darkened moment.
Catch the stillness. Performers can be stunning while at rest between moments of movement. Don't miss out on these images.