Teach me how to scream?

Ok. Alot of us know Lacey from Flyleaf; And alot of us know that she's only like THEE BEST FEMALE SCREAMER EVER!!!!!!!! And I'd like to learn how to scream like her (not literally, lol) so can anyone give me any pointers 或者 refer me to any ututorials 或者 something? Thanks! :3D
<--mustache-man-->