Check your faucets. A drop a second can waste hundreds of gallons of hot water a year and waste the energy it took to heat it. If you don't need a light, turn it off. Unnecessary lighting adds unneeded heat in the summer and can add up to a sizeable expense. Low-volume shower heads maintain the full force of your shower while reducing the amount of water used.
Drafts are a major source of energy waster.
Cover windows with plastic. Insulate doors with insulation lining. Fireplaces are extremely inefficient and usually take away more heat than they produce. Keep them to a minimum.