Lighting is very important. Portable spotlights, with blue lens covers, shed a ghostly cast. Swapping standard outside house bulbs with yellow, orange, or green bulbs achieves an eerie effect. For an exotic glow, station black lights where trick or treaters come knocking. Merely turning lights upside down can be effective also.
Sound effects add a spine-tingling edge to spooky surroundings.
Station stereo speakers in bushes or at open windows. Shrieking cats, creaking doors, crashing thunder and screams and moans can all be found in cassettes or CD's in many stores. No, they are just a couple of penlight flashlights with lenses painted red with thinned nail polish, snuggled together with electrical tape, and suspended on broken rubber bands. Another creepy effect can be made with regular flashlights. Spray paint the bodies black, but leave the colored collars.