Make sure the thermostat is protected from a heating / cooling source
Basically, make sure the thermostat location isn’t too hot, or too drafty. The thermostat measures the temperature and locating it in either location can throw off the reading.
The effects can be disastrous for your utility bill.
The area might be warm, so the thermostat will be tricked into thinking the heat has done its job and turn it off. Actually, just the area where the thermostat is located is warm because it is directly over or very close to a heating vent.
The opposite is true as well. If the area is drafty, the thermostat will keep the furnace on longer, heating the whole house unnecessarily. And this costs money. More money than you need to spend on heating.
Keep the unit shielded from direct sunlight, as this can also affect the reading.
The same holds true in the summer. If the thermostat is placed in a sunny or warm location, it will keep the A/C on unnecessarily. Sometimes, you might even forget the A/C is on and open a window to let the warm summer air in to moderate the temperature!