My favorite scare has always been the classic "sit still until they think you're a prop, then start moving" trick. I got to a lady last year, just as she finished saying to her companion, "You know what they need is somebody to jump out at you right here." She was looking right at me as she said it. She freaked when I stood up, and the guy about died laughing.
So, simple is good. Setting up their expectations, then flipping them on their heads.
Another favorite? People really don't like it when you follow them. You're supposed to stay on your property, the street is supposed to be safe. The car is supposed to be safe. I'm not advocating for chasing people into traffic, but there is a certain charm in walking slowly and with purpose behind a group of teenagers screaming "it's following us!!"
Again, defying expectations.
As far as actual props go, it's hard to beat lights and fog. Some carefully directed lights, or one of those laser light show machines, and a creeping wall of fog does a lot to set the mood.
If you need some kind of large structure, ask around at appliance stores for a refrigerator box. It's big, a person can fit comfortably inside, and it's already built. We made a fortune teller booth from one, just by making a couple of cut-outs and painting. There was a rather long line.
And don't underestimate the effect of some creepy, gauzey ghost like figure hung from a tree limb. There's one we always put out so that it is lit by the street light, and seems to be a perennial favorite of the neighbors.