Although I've not actually done stage work myself, it seems to me that the consistent element in the exceptional stage images I've seen has been metering/exposing for the highlights, and letting the shadows fall where they may (translation - fast glass). That, and excellent timing - where it's obvious the photographer was in sync with the rhythm of the presentation, and was thus able to capture just the right moment to convey the story behind the ballet as well as the mood/emotion of the dancers.

Depending on where you will be located during the performance, it would be good to go there in advance to get a feel for what the compositions will include considering the lenses you'll be using. That way, you can develop at least a skeleton of a plan. Being able to at least meter the areas of the stage in advance would be helpful, too, I'd think. That way, you can set exposure based on the area of the stage being photographed, rather than having to try to meter each shot. Making a little diagram of the light-level zones might be helpful in that respect.