Steps
1. Listen to any album using harsh vocal techniques. If you're not already familiar with the genre, browse the links listed below. Buy CDs from bands and singers whose voices you admire.
2. Warm up for your voice for 30 minutes. You should use "oohhhhhs & aahhhhs" to find your range and warm up with. Then progress into clear vocals. Start quietly and get louder as you can. See the related wikiHow on singing properly, or consult singing resources. This will help ensure that your voice stays healthy and strong.
3. Hum with your lips closed. If it vibrates, you're good. Then with an open throat and mouth, go through your "ahhhs and oohhhhhs". Use your diaphragm.
4. Sing a note within your range, then try forcing air up from your lungs and pushing out hard with your chest (almost like you're vomiting). Then return to a clear note.
5. Experiment with your voice. Find your range using the "ohhhhs and aahhhhs". You must be able to hit the notes singing clear to sing them in a harsh vocal.
hook em horns... bless you internets:
http://www.wikihow.com/Do-Harsh-Death-Metal-Vocals