The secret is the element of surprise and reality instead the same hokey predictable stuff. That's easier said then done.
Having Elvira giving out kisses in front of the girlfriend then leaving blood would be funny.
Having someone mug another actor would be scary.
Instead of the old man in the coffin sitting up, the coffin opens up empty, but the corpse comes in behind you when they are looking at the coffin open.
An electrical failure would be scary, out go the lights in utter blackness, you have someone saying not to panic with a flashlight. Have a girl scream in the dark.
Anything totally unexpected and seemingly real.