As an Heating and A/C technician, I have various tips up my sleeve to help with lowering the cost of your monthly utility bill, the first tip is to only run your central air conditioner or furnace when you are home, many times people will forget to turn off the air conditioner or heat when they leave for an extended period of time, and this will only make your utility bill go up.
How many people like to keep their central air conditioner or furnace running throughout the day while they are at work so that they can come home to an air conditioner or warm home, and for these people I would suggest getting a smart thermostat so that you can set up a schedule that will cause your central air conditioner or boiler to turn off when you are at work, and to turn on when you are on your way home! Another suggestion is to keep your windows and doors shut while the Heating and A/C units are running.
Many times kids will open a window in the house and forget to shut it, causing the cool air from your mini split air conditioner, or the heat from your hot water boiler to go outside rather than do its job of heating or cooling your home. Some summertime afternoons it is nice to open the door and let the fresh air flow through the house. If this is the case, just go to your control machine and turn off the air conditioner so you are not wasting energy and money. These are just two simple ways to keep Heating and A/C costs low.