Do the candles on your table gutter in a steady breeze, even though none of the windows are open? Can you see tumbleweeds drifting across the hall? Are your drapes swinging ethereally? Your house might be haunted...but it's probably just drafty, and that's going to drive your heating bills way up, way fast. It's time to say goodbye to drafts for 2014, because you deserve better than eight layers of blankets and chattering teeth every time the mercury drops.
If you have a draft problem in your house, chances are you have a rough idea of where the problem's originating, but take a closer look. Common culprits are doors and windows, both of which tend to expand and contract (along with their frames) when temperature and humidity levels change. Over time, that can lead to permanent warping, which creates openings for cold air to come howling in. Inside the house, it's common for drafts to creep in under doors, making it hard to control the temperature from room to room.
Poorly insulated homes can develop drafts from small openings to the inside courtesy of worn siding and roofing (another good reason to have your roof inspected and consider adding attic insulation if you haven't done so already). Another possible source is your chimney, which isn't supposed to let cold air in, but might be doing just that if it's not properly maintained or you're leaving the flue wide open.
At Grist, Umbra notes that electrical receptacles, plates, and switches can be another source of drafts, as can vents. If you live in an area where you need air conditioning in the summer and you use a window-mounted unit, that's another potential source of problems, as air may be leaking in around improper seals.
Windows and doors are a good first line of attack for handling drafts. Add weather stripping to further insulate them, and consider using heavy curtains on windows to limit both drafts and heat loss through the windows themselves. You can also add draft catchers to the bottoms of your doors: fill an old sock or a simple fabric tube with beans, rice, or some other stuffing material and run it along the bottom of the door. This will block gusts of cold air and help you stabilize the interior temperature.