Windows and DOORS
Seal up any drafts around windows and doors to keep warm air inside and cold air out.
Insulation
Insulate your attic and walls to keep heat from escaping. A little caulk goes a long way...
Cover all windows
Use heavy curtains or window coverings to keep heat in at night. Covering windows with plastic also does wonders!
Don't neglect this!
Keep your furnace or boiler maintained to ensure it's running efficiently. Basic maintenance can make a big difference in performance.
The Thermostat
Use a programmable thermostat to regulate the temperature in your home. It's a relatively inexpensive cost, and it can save you a ton of money!
RUGS AND CARPET
Add rugs or carpets to hardwood or tile floors to insulate and add warmth to your home.