I generally place the mic about even with the eyes so the singer has to look forward (tend to breath better) and start with a distance from the pop filter/screen by having the singer place they're hand over their mouth and point their elbow at the mic.... and no closer
really strong vocalists I make back up until I get a good solid level that they're clipping.... if someone clips consistently I will try a different mic (mainly condensers) and possibly place a compressor in the signal chain - be careful
(or if a screamer) change to a dynamic mic
I have a strong voice and typical stand ~ 3 feet away from the mic
getting too close causes issues with proximity effect (low freqs become inaccurate)
