Fill leaks around window frames and exterior walls with caulk.
Keep the air vents clear of draperies, furniture and obstructions that will block airflow from heating or A/C.
On the side(s) of your house where the sun shines, open the drapes, curtains and blinds during the day to let the sun shine in. Close them at night to help keep the warm air in.
Replace your old thermostat with a programmable thermostat (also called a 'set back' thermostat). Look for one with the Energy Star label.
Seal leaks between doors and their frames with weather stripping.
In the Winter Season, set your thermostat at 68 degrees when the house is occupied and 60 degrees when you are away from home. In the Summer Season, set it to 78 degrees. Every degree can save three percent off your heating bill.