1. Prevention: Drink a couple of pints of water over the hour before showtime.
2. Practice: Do exercises to get you singing from the diaphragm. Your throat is the bit that holds the vocal chords, not the muscle that pushes air past them.
3. Remedy: Honey by the spoonful - manuka is antibacterial if you don't want tooth decay from cough sweets.
4. Recovery: Then there's the one where you chop an onion, cover it with brown sugar and leave it covered overnight. Drink the brown syrup that results (not all that bad actually). Poor man's Covonia which is supposed to bring your voice back YMMV.

Alcohol might help in relaxing the throat, I don't know. It certainly relaxes the brain.