Every month, change your furnace filter. It’s a minimal expense but important for the efficient use of your furnace. Purchase filters ahead of time, either 6 months or a year, so that you never run out. Store the size and brand in your smartphone or write it in your planner.
If you own rental units, purchase these for your tenants or schedule your visits around the time to swap these out yourself. It will be worth it over the long run.