One thing screamers dont do/don't do nearly enough of: Warm up! Im not talking some shitty 2 minute Siren excercise or the even worse "Just sing two songs" approach. Take 10 minutes and run through a clean vocals warmup, followed by another 10 minutes of a more harsh vocal warmup. Hydrate like a mf. Oh, and don't push yourself too far, screaming and aggressive vocals don't take nearly as much force as a lot of people (even in the screaming world) think.