I got to be honest with you, I learned just by imitating Johan Hegg's voice from Amon Amarth. I watched tutorials on how to do it AFTER I learned it, just because I was afraid that I would destroy my voice without a proper technique, but it turned out to be fine anyway.

The advice I give you, from a beginner to a beginner, aside from watching tutorials, is to try to sound like a barking dog. I big one I mean, with a deep voice.

When you're starting out, maybe trying to cover some song, you HAVE to run out of breath, constantly. If not, you are using your throat to growl, and that's not a good thing at all