Determine your vocal range before you start to scream-sing. With a piano or guitar, hum along from a mid-range note to as low as you can comfortably and accurately sing, then as high as you can comfortably and accurately sing. Trying to sing outside of this range can damage your vocal chords.
Warm up before you sing, especially for scream-singing. Sing scales or short songs that cover your range.
Make growling noises to test the most comfortable way to sing. When you growl using the back of your throat, like a cat, your vocal chords will probably tire out quickly and make your throat sore. Try making more nasal growls, like Marge Simpson on “The Simpsons.” Once you master the nasal growl, try doing in louder. Then try singing in this kind of growl. This will produce a scream-singing.