Control the summer sun.
Keep curtains and drapes drawn during the day in the warm months to block out the sun’s heat. White blinds and/or draperies will also do a better job of reflecting the sun light from your windows.
Use the sun in winter.
During colder months, open south and west facing blinds/draperies to let in radiant sunlight and take a load off your furnace.
Make sure you have adequate weather stripping on your windows and doors, and keep them closed when running your AC or furnace.