Heating and air conditioning are usually the largest loads in a home and responsible for 40-50% off your monthly energy bill.

Thermostat

Set your thermostat to 78^oF in the summer and 68^oF in the winter. A one degree increase or decrease can increase energy use by 3-5%.
Install a programmable thermostat to save even more.
When using the fireplace, turn down your heating system thermostat.

Change central HVAC system filter by manufacturer recommendation, or when dirty. Dirty filters can impact your home comfort and increase your electric bill.
When installing new air filters, make sure they are facing in the correct direction of air flow (look for the arrow on the side of the filter).
When heating or cooling, keep windows locked.
Do not close off unused rooms that are conditioned by forced-air systems.
Do not close supply air registers.
Make sure outside soffit vents are not blocked.
Do not use roof-top power ventilators for attic exhaust as they may draw conditioned air from your home.
Have your HVAC system serviced yearly by a NATE-certified technician.
Monitor your home's relative humidity in the summer. If it consistently stays in the 60% range or higher, ask your HVAC technician about lowering your central air conditioning unit's indoor fan speed.
Remove and clean filters on window units monthly.
Keep "fresh-air" vents on window A/C units closed.
Ensure your outdoor heat pump/air conditioning unit is kept clean and free of debris.
Ensure floor registers are not blocked with rugs, drapes or furniture.

Run ceiling fans counterclockwise on medium to push cool air down.
Close shades and drapes during the heat of the day to help your home stay cool.
Turn off fans when not in the room. Fans cool people, not rooms.
Plant trees and shrubs to provide shade on the east, south and west sides of your home.

Minimize use of electric space heaters, except for limited or temporary spot heating. Turn space heaters off when leaving the room. An electric space heater can cost more than $100 per month to operate.
Adjust ceiling fans to spin clockwise to bring warm air down.
Open shades and drapes on sunny days to allow the sun to warm your home.
Close shades and drapes at night to keep heat in your home.
Remove window A/C units and close and lock the window.
Use heavy-duty, clear sheets of plastic sealed tightly on the inside of windows to reduce the amount of cold air entering your home.
When using the fireplace, open the outside air vent in the fireplace (if provided) or open the nearest window slightly. Keep fireplace dampers closed unless a fire is burning.