Investing in a book or two would be a good start as well as the lessons notion. The more you read into something the better your knowledge of how it's supposed to be done will be. If you have a good teacher to go with that then they can instruct you when you stray from the path of proper performance, but you're not going to find a teacher or any books that inform you how to growl or scream and most likely you won't find very many singing websites that smile upon it either. Just be careful with the growling part or else you'll end up like the vocalist of In Flames (yes I know you referenced them and no I'm not taking a jab) and completely ruin your singing as well as your growling voice. People that treat their voices like he treats his have a future of progressively worsening technique. It's the equivelant of a guitarist with carpell tunnel syndrom continuously playing while never getting his wrists checked out. And the scenario is even more of an issue if you're growling since the vocal style is so much more aggressive. It's super easy to damage your vocal chords by doing so. Yeah, that's about the extent of my knowledge on being a vocalist. It's a lot more of a handle with care thing than I think most people realize and when people like Anders Friden and Chris Barnes are both good examples of how poor care in general let alone with a more aggressive style can really cost you in the future.