Sorry if I am not as witty as some of the others but....
First off give yourself a decent level. I try to do at least -6 like Roc but when I am tracking I use a manley voxbox or an LA610 so I can utilize the compressor.
Remember when you turn up a live track that was recorded at a low level you might be also turning up some of the extra room noise that the mic has picked up. Make sure your artist is in the correct position in the microphone so you are not having to crank the preamps. Also be careful how loud you have them in the phones. When the vocal track is loud in the phones they sometimes sing at a lower level. This ends up giving you a poor performance out of the artist, headphone bleed and extra room noise.
I realize this is more than what you asked but I think all things should be considered when tracking with a mic.