What I usually do is drink lots of tea with lemon and honey, and speak like Elmer Fudd. If I have a stuffy nose aswell I make a lot of hollow 'Mmm' and 'Nnn' sounds. It seems to relax the throat and clear the sinuses.

I also used to sing everything down a semitone or two, but that usually made things worse, because I was not used to singing in those keys, so that made it more stressfull on my throat.

But the best remedy is sing as little as possible, and rest your voice. But we all know that it is not always an option...

Doc-Z