Learn how to sing properly in order to sing death metal. Although most death metal is often not sung in a particular key, learning how to sing in a traditional manner will help you project and use your diaphragm properly while grunting. Learn how to sing in key so that you understand which notes you are grunting when you start your death-metal vocals. Employ a vocal coach who understands the death-metal genre and can help you improve as a death-metal as well as traditional singer.
Learn the proper way to breathe. Death-metal vocals are very deep in pitch, so learning how to control your breath properly will make you a better, stronger death-metal singer. Practice breathing exercises such as blowing a feather up in the air and concentrate on pulling your breath deep into your lungs. Exhaling should be controlled as well, as that is when the sound is created.
Keep your vocals cords lubricated. Warn liquids such as tea and room-temperature water will keep your throat from closing up when you start grunting. If you employ a higher voice, like many of the more popular death-metal singers such as Corpsegrinder from Cannibal Corpse or Glen Benton from Deicide, keeping your vocal cords lubricated will make it easier to switch between the two voices when you are onstage or at practice.
Warm up before all gigs. Warming up will prepare your vocal cords for the strenuous task of singing death metal. Come up with a ritual that covers all ranges that you sing in, but make sure you do not overdo it as you may strain your vocal cords when you start to vocalize on stage or at practice. Go light on the aggression and concentrate on your breathing as well.
Relax and refrain from speaking much after the show or practice. This will prevent your vocals cords from swelling or voice blowing out. This is particularly important if you have another show the next day. The more you rest your voice afterward, the stronger you will be vocally the next day. Drink more fluids after the concert or practice to keep those vocal cords lubricated.