For cooling, set the thermostat at 78 degrees Fahrenheit during the day and turn it up or off when you are away or on vacation.
Install a clock thermostat for your heating/AC system that turns the AC setting up automatically when you are away and brings the temperature back to a comfortable level before you return or get up.
Close draperies to keep the sunshine out on bright days. Consider using insulated draperies and shades. Open windows at night when temperatures drop into the 60s.
Insulate to keep the heat out of your living space. The attic is one of the most important places to insulate. The insulation's R-value is the measure of how well insulation keeps warm air from escaping through it. The higher the number, the greater the insulating value.
Stop air leaks and cut air drafts. Gaps and holes where plumbing pipes and wires enter the home and around exhaust fans and vents as they exit the home should be caulked and stuffed with insulation. If you can see daylight or feel a draft through a crack under or over a door, you may want to consider weather stripping.
Plant shade trees on the south and west sides of your home, but not directly under electric wires.
Invest in a more efficient air conditioning system. Air conditioners with a higher SEER rating are more efficient and less costly to operate.
If you have a fireplace, keep the damper closed. Glass doors on the fireplace can help stop air leakage.