We like having the trick or treaters come to our door, and seeing their costumes. We put lots of candles and decorations outside, and seeing what Christmas decorations we can pass off as being for Halloween. I have a camping lantern with a flashing mode, which I put behind a ghost picture.
We like scary games, and were inspired by the skeletons in the book Funnybones frightening each other. In turn, each of us is blindfolded, led around the garden (weather permitting), and scared by the others for a few minutes, with things like squirting with a water pistol, putting hands in something slimy (e.g. eyeball grapes), ghostly noises, being touched unexpectedly. A timer is set for five minutes for each person: the brave winners are those who keep their eyes covered the whole time! (We take care not to seriously freak each other out.)
Another game we like is "zombies". The first zombie is blindfolded, and stands with their hand outstretched. In turn, the other players tap the zombie's hand; and the zombie tries to grab the hand. If anybody is grabbed, even by the finger, they become a blindfolded zombie as well. The others then have to tap each hand in turn. The winner is the last player left, who becomes the next zombie.