People will tell you to "sing from your gut" which is true to a degree. Just remember, no matter where your energy is pushed from, your vocal chords make the sound, so keep the throat in good shape.
When we record, I do ALL my growls in one day. I do them first, then I record all my clean spoken vocals right after, because at this time, your throat is so loose, you voice really drops low, and gives you that deep soothing sound, GREAT for spoken word stuff. Then i take several days off, and return to actually "sing". Another point was made to use a buffer for your vocal chords... The last CD, I went through two 2 liters of Coke, making sure to drink after every verse to keep it well moist. And, you get a really cool "wet" sound to your voice.
Well, that how I do it, and with that growl, I try to pronounce every word as clear as I possible can. Check out the mp3s if you get a chance.