I am the vocalist of two bands (see sig). Both are death metal, so I growl mostly, but I never took any lessons for it (there aren't many people teaching growling-techniques...). Some common sense and a bit of warm-up has been good enough for me. With common sense I mean things like:
* Don't start screaming away without any kind of warmup, you'll rip your throat up even if you don't do death vox.
* Use your gut muscles to sing, you should feel them becoming tense when you hold your hands on your sides while singing.
* Don't do shit that hurts. So what if you don't hit the perfect note? At least you'll be able to keep on singing...
* Don't smoke.
* Drink a lot to moisten your vocal chords when singing. Not too cold though.
* Have fun.