* Drink lots of water. Avoid alcohol, caffeine, dairy, and sugar.  Alcohol and caffeine dehydrate the body and your throat.  Dairy and sugar excite enzymes that lead to mucus production, etc. that have an adverse effect on the throat.

* Bring a copy of all lyrics, and make sure backing vocals are worked out in advance.  If you bring them on a tablet (like an iPad or something), you can scroll silently and not have to worry about the sounds of papers rustling, falling, or turning!

* Warm up your voice prior to singing.

* Get a good night's sleep!  A tired voice breaks easily.  Physical energy translates into performance energy.