green tea with lemon and honey does wonders for an already blown voice. i sing in a crust band and do black metal croaks mixed with grind gutterals.
as for preventative measures, i usually drink 211 while playing, it coats the throat real nice. i've also heard of some brutal death metal vocalists eating cheetos to coat their throats, being a vegan i've never tried it, but the person who told me about it does pretty sick vocals. also try singing from your diaphragm rather than screaming through your throat. there's plenty of videos online about mastering that technique.
oh yeah, i had a gnarly infection in my throat once while i was still at my moms house and she made me a lemon and garlic tea mixture that tasted like shit, but i'll be damned if it didn't make my throat feel 1000x better.