Sing every day to keep your range and tone in good shape. Sing scales and arpeggios that take you from the lowest part of your range to the highest.

Warm up by humming then singing Ah or La scales, then one of the songs you plan to perform.

I agree with Len's avoid list, but for some people, especially in dry climates like the one where I live, milk is a GOOD thing for your throat. Milk can help keep the tissues from drying out too much. If your throat feels dry or you are in a place where the air is drying, drink a little milk while you are exercising your voice.

Alice Flynn