i evaluate each group and then do what experience tells me will work best for them. Sometimes it's jump out and boo, other times it's a dialog/funny conversation, or just creep out scares or whatnot.. I try to tailor it as much to the group as possible, and I listen to the actor in front of me that they encounter first, because that can give you a very valuable clue.
This question is kind of like asking a programmer how to write code. Your response will vary greatly.