Dedication and commitment to the job for one, and creativity with an open mind. Can't hold back on the performance.
Definately commitment. If your mind isn't into what you're doing, aka: haunting, you're not going to convey the element of "scary". I mean, like if you're a zombie and you aren't trying to eat people's brains, everyone's going to know there's something wrong. Think scary thoughts. Periodically 'boo' at passerby or something to keep your head in the game, so to speak. Even if your head becomes detatched for ANY reason. Also, you could try using your prop or whatever you have to startle people; a few swings of a scythe or some rattles of a chain. A bite or two is customary if you're a vampire. And finally, actually ACT scary. Don't just say "boo" in a monotone voice or anything. Make every 'boo' count, draw it out. Make your voice scary "BOOOOO...." WITH VIGOR! Also,
