Unless you are still operating a wood-burning stove or use blocks of ice to cool your living space, chances are you have a modern, programmable thermostat. Many people already realize that programming their thermostat to maintain a higher temperature for AC or a lower temperature for heating during the day while they are at work will save money on energy. Think about it - the less the unit has to kick on during the day, the less energy it expends, and therefore you pay less money. But when you come home from work, think twice about cranking the air conditioning all the way back down. Do you really need every space in your home to be that cool, all evening? If you are only occupying the first floor of your home for the majority of the night, try leaving the air up a few degrees....remember that warm air rises, so chances are you can cool a first floor with less AC and with a small fan, if you are a little warm (a floor or table fan still uses less energy than a full-blown air conditioning unit).
One thing you might not realize is that anything you place around your thermostat also impacts its sensors. A modern thermostat is quite sensitive, so if you have a lamp or electrical equipment near it, it might think the room is warmer than it actually is, and force extra air out to make up the difference. The opposite effect will occur if you have something near or around the thermostat that would act as insulation. It might think the room is perfectly fine while you are either freezing or burning up.
So, in short, pay attention to your thermostat! It needs maintenance just like any other piece of technology in your home, and when dealt with carefully, it could save you lots of money.