I started out trying to do black metal-style vocals, which are way easier to do than guttural stuff. Once I got that down, I started working on my growls, which are a similar technique (at least for me) in a different part of the throat. Like other people have already said, go from your abdomen, and try to get a good coating of phlegm or something else, as it'll protect your vocal chords. I smoke a lot, which I think helps, but I wouldn't recommend smoking just to get a better metal voice.