Usually you try to group similar spells to the same keypress, like mind flay and life drain, and use round robin howl or terror/psyschic scream on the same button. You'd probably want at least 1 button left for just shadow bolt spamming and keep mind blast on a different one. I've never played a lock or priest though but when multiboxing the main thing to remember is that similar spells have to be grouped! Also make sure you use a [nochanneling] modifier.