I've had times when the voice had to work or the job was lost. Here's some of the things I do: Humidify during sleep.

GET REST.

Drink gallons of ginger root and thyme tea sweetened with honey. Use Fishermans Friends, but sparingly. They can burn.

Always warm up for at least 15 minutes before going on.

Avoid things like Chloroseptic which deadens the throat and can lead to serious damage to the vocal folds by making over-singing too easy.

Lots of diction exercises to warm up and loosen up all the parts of the body that produce sound: hips, diaphragm, lungs, neck, throat, tongue, lips, upper palate.

There. I'm done.