1. Get alot of volume. Volume is Power. Metal is angry.
2. Sing with your Diaphraghm (lower stomach) It will sound alot better, deeper, and louder. Sometimes you can sing with your throat for really high screams though.
3. Try expanding your vocal range by starting out at the low end and raising the tone till you cant go higher, and then back down. (repeat) Your voice should crack somewhere along the way, which is normal but not a good thing to have. Everyone has this problem, but if you do this exercise, you'll end up with a wide vocal range.
4. Experiment. It's your godamn voice. Not mine. Dont try and sing like me or anyone else... sing however you want, but do it in your own style.
5. If you play guitar, try matching your voice with a note. This will help you get on key.
I hope this helped, if you have questions or whatever, PM me.