10. Cover windows.
At best, windows do a marginal job of keeping the cold outside. Insulated shades and curtains or even homemade insulated panels can help, especially at night. Just remember not to block the light (and solar heat) during the day.
11. Insulate above the basement or crawlspace.
If area rugs (item 9) don't cut it, consider insulating the floor over an unheated basement or crawlspace, creating a simple thermal barrier between your living spaces and the 55-ish-degree air down below.
12. Get an energy audit.
An inexpensive (often subsidized) professional test for air leaks, insulation levels and other thermal performance factors is the best way to learn where the cold is getting into your house.