Have leaking windows and doors, seal them in easy to prevent cool air from the AC from getting out and hot air from the heater getting out. Leaking heat and cold air is a major waste of electricity spewing the air you have just spent cooling or heating to get out of the home.
Most homes can be checked for leaks in either cooling or heating through the use of FLIR equipment which recognizes the differences in temperature, say the hot air seeping through the door jamb. Or the non-energy efficient windows that may have escaped upgrades to your home. the gadget is a nifty thing to use but it is quite expensive so tool rentals would be the best option for you.