Make sure your fireplace is properly vented. Fireplaces require a great deal of oxygen. If you do not have an outside source of combustion air, your fireplace will draw air from inside your house, including the air you paid to heat. Ensure all return air openings are unobstructed. Don't block heating registers, move furniture to allow heat to flow freely.
Unoccupied homes use more fuel to maintain the same constant temperature level than when occupied.
During occupancy such items as lights, greater refrigeration operation, cooking, radio and TV, dishwashing, hot showers, and bathing and even the occupant bodies add heat to a room. Close them at night to keep out the cold. Avoid changing the thermostat setting frequently. Have your thermostat placed on an indoor wall in the place you spend the most time in your home. It should never be placed by an outside door.