If it is very bad, like your voice is almost gone, don't sing and just rest it out and let it run it's course.

If it is like a thick throat that gets better when you clear it. Just do a good warm-up routine and you should be ok. Avoid falsettos, and try to do some "Elmer Fudd" impressions, and hum scales so that your nose and pallet vibrates. That is a good start.

Hope you feel better.

Cheers!

DocZ