Get an energy audit.
A properly executed audit1 will pinpoint your energy-loss flaws. The prime culprits tend to be underinsulation, duct leakage, and outdoor air infiltration. In addition to having an efficient, properly functioning heating, ventilation, and air-conditioning (HVAC) system, fixing these deficiencies is often the most effective way to reduce your resource consumption.
Get with the program.
Having an efficient HVAC system is smart.2 Not having a programmable thermostat to properly utilize said HVAC system is dumb.3
Make every effort to utilize your HVAC system only as a last resort. Open windows to create cross ventilation and supplement the effect with fans.
Shun the sun.
Unwanted solar gain in hot months results in unwanted increases in energy bills. Exterior awnings and indoor window treatments can add to the design of your home while blocking rays.