Set back your thermostat 2-3 degrees lower at night because your greatest heat loss occurs at night.

Invest in a programmable thermostat. By doing so, you can program the thermostat to turn down your air conditioning/heat for you when you leave for work when no one is home and after you go to bed when everyone is asleep. A programmable thermostat can run anywhere from $110 to $550 installed.

Replace your filters every 30 to 60 days. If you have a permanent filter, clean it with a mild detergent, per manufacturer's recommendations, every 30 to 60 days.

In the winter, when it's sunny out, open up the shades to let the sunshine in and heat your home. In the summer, close the shades to keep the warm sunshine out so your air conditioner doesn't have to work as hard.

If your furnace and air conditioning units are over 15 years old, consider replacing them with newer, high efficient units. Doing so can cut your gas and electric bills nearly in half.

Change your filter monthly!
This will give you better airflow, heat or cool your house quicker, provide less stress on the equipment, & filter the air so you don't have as much dust.

Clean your drain lines
The hoses connected to your furnace can develop "build up" inside them over time. If it gets bad enough, water can back up into the furnace and cause damage. Pour bleach through the lines and make sure liquid is getting through to the drain. Use caution with any cleaning agents that might be harmful to your skin or eyes.

Change the batteries in your digital thermostat annually
People forget that their digital thermostat has batteries in it. If you get in the habit of changing the batteries annually, you can eliminate a no-heat situation.