1. Clean and maintain your heating and air conditioning system.
Follow the manufacturer's instructions for cleaning and maintenance for your appliance(s) for general tips on extending the lifetime of heating and a/c devices, saving money on monthly bills, conserving energy, and reducing the number of emergency repair calls you have to make.
2. Decide where to set the thermostat.
He likes it hot, so he nudges the thermostat up. She likes it cold, so she nudges it down. If this kind of disagreement becomes a point of interpersonal friction, some families (or office "families") can put a lot of wear and tear on a heat pump, switching the heater or air conditioner on and off...or even switching back and forth between both of them when the outside temperature is actually comfortable. Who needs thermostat drama? Save money by choosing a temperature and leaving the thermostat there when people are inside, setting the thermostat for minimal temperature control when everybody leaves the building. (It's usually easier to set the thermostat low and let chilly people put on sweaters, but if you want to set the thermostat high, in summer, and go clothing-optional, that's up to you.)
3. Dehumidify if necessary.
It's possible for air to be too dry, but if the view outdoors is lush and green and mold tends to form in dark closets or basements, the air is probably too moist. Throat and sinus problems can be caused either by irritation from dry air, or by allergy reactions to mold spores in damp air. Damp air may also cause people to perspire more, feeling clammy-chilly or sweaty-hot even at optimal temperature settings. A dehumidifier warms the air slightly, reduces the humidity significantly, and uses less energy than a heat pump.
4. Seal climate-controlled air inside.
Buildings do need some degree of air exchange, but that's a less common problem. A cold day is a good time to check for air leakage around windows, doors, damaged walls, and through roofs. Add caulking, weatherstripping, and insulation as indicated. Insulated roofs reduce the need for air conditioning in summer.
5. Upgrade to more efficient devices.
Choose heating and air conditioning devices (and other appliances, including refrigerators and computers) that have an Energy Star. Don't overlook lights--inefficient lighting can raise a building's air conditioning needs. Remember that although the Energy Star identifies the most efficient appliances in a class, the class may be bigger or smaller than you need, so shop carefully to avoid waste.
When you buy new devices, it's crucial that they be properly installed by professionals. Incorrect installation could reduce energy efficiency or even compromise the safety of large appliances like heat pumps. Consult professional heating and air conditioning service people for your heating and ac repair needs.