Heads up, cool kids: Math is way hip. Particularly, geometry, facets, and gem shapes have been everywhere designy for the last two years, and there's no reason the holidays shouldn't be included in the trend.
Case in point: this geometric garland. It looks nice and handmade, is holiday-neutral, and the colors are winter-y enough that you could leave it up through February.
Unless you're ready to go full out, it's kinda hard to decorate for Halloween. Anytime I've tried, my house has looked like 1) a crappy, half-finished haunted house, 2) like the clearance aisle at the discount store on November 2nd, or 3) like a kindergarten classroom.
But, wait. Hold up. What about something that's Halloween-y, but doesn't resort to overplayed imagery, and even includes a bit o' nostalgia and pop culture imagery to boot?