Homeowners often do not keep up on HVAC maintenance. This included changing the air filter twice a year. It will cause the fan to overwork and possibly burn out if not done.
Smart thermostats are excellent. They are usually easier to use than programmable thermostats. There is also the benefit of keeping an eye on temperature and humidity in the home while you are away.
If you have single-pane windows, you should consider upgrading to a quality double-pane window. Single-pane windows lose too much energy and allow air and sound to pass easily.
This is especially important for hot water. If you have high-flow water fixtures and use hot water, then the water heater has to heat a lot more. If you have well-water, the well-pump will also run more, even with cold water.