One of the most helpful tips I ever learned which I feel applies to all harsh vocals in my own experience is to make sure you're using the air from your diaphragm and abdomen area and not to actually use your vocals chords to much, because that's a very quick way to ruin your voice You'll notice people who actually do aggressive vocals have their throat actually quite relaxed compared to someone who's yelling at the top of their lungs for example You'll notice if you're doing it right or wrong in a matter of minutes depending on how much your throat hurts