There's not much that says "unprofessional" like shaky hand-held footage of a stage play. Putting your camera on a sturdy tripod will not only save your arm, but it will make your footage look much better. A fluid head will allow for smooth pans. At the very least, use a monopod.
The easiest way to do it, and the one that involves the least amount of post-production work, is to shoot with multiple cameras and a switcher and edit "on the fly". Ideally you'd have one camera on a wide shot, and one or two other cameras hunting out close-ups and medium shots. However, three cameras, two camera operators and the requisite cables and switching equipment aren't in everyone's closet-o'-video-gear. If you can't use three cameras, use two. If you can't use two cameras, try and shoot the show at least twice.
Shooting a play with a single camera opens you up to a host of problems: Static shots are boring; if you're moving and following the action you may miss something going on elsewhere; but the biggest pitfall is that left to a single camera, people have a tendency to firehose and motorzoom. Firehosing is when the camera swishes back and forth across the action, back and forth between people who are talking or a conductor and the violinist (like a firefighter trying to put out a burning building) and motorzooming is rapidly zooming in and out. Make your camera movements calculated and resist the urge to put too much movement in them. Zooming should be done sparingly and for a reason. Let the subject's movement control the action.
B-roll is, of course, stuff other than the main event which could conceivably be happening at the same time. It can be people sitting in the audience (mom and dad looking proud), a close up of a detail on the stage, the conductor from a different angle, etc. Having B-roll means that if you make a mistake during videotaping, or you need to change your zoom angle, you can cover it up in post production.
Stage lighting isn't about accuracy, it's about mood - and for that reason, you'll find lights in many unique colors on a stage and the lighting designer might want the whole set bathed in blue, or red, for effect and it may change between scenes. None of this will serve to help your camera figure out what should be white. The best thing to do is use the camera's preset for tungsten and let it go.
