If you have carpets and rugs, sprinkle them with baking soda and give them a good hearty vacuuming. Make sure you move the furniture around and clean beneath each piece -- it's time to get all the yuck out of your house, and dustbunnies are notorious for getting in the corners under the couch. If you have an extender on your vacuum cleaner, use it to suck up cobwebs and dust from the ceiling fans, baseboards, and other hard-to-reach spots.
Use a broom to sweep out any little bits of dirt and grime -- it's also a symbolic way of sweeping negative energy out of your home.
If you've got a filter on your home's heating system, now's a good time to replace it with a new, fresh one.
Do you have hardwood floors instead of carpet? Use an environmentally-friendly cleaner to get rid of dirt and grime. Clean baseboards and other woodwork.
Get your bathroom clean. It's a place in our house we try not to think about unless we're using it, but there are few things more impressive than a clean bathroom. Scrub toilets, wipe down countertops, and spray out your bathtub.