I'm reposting this from 2 years ago to join Kristin today for Thrifty Thursday. Be sure to hop over to her blog each Thursday for more great tips!
If you spend most of your time in the room that has the thermostat, run the fan in that room. The fan will make the room a degree or so cooler, which will make the thermostat run less throughout the whole house. For that matter, a fan in any room will make the room seem cooler, which means you can usually crank up the thermostat a degree or so higher.