If you live in the northern hemisphere and haven't yet switched the direction of your ceiling fan's blades, now's the time to do so. You want to make sure that the blades' direction is switched from moving in a counterclockwise direction to a clockwise direction.
To do so, just flip the switch at the base so that the blades rotate clockwise (that's when you're looking up at it from below). By switching your fan's rotation seasonally, you can save 10-15 percent on your heating bill and as much as 40 percent on your cooling bill in the Summer. Plus, it will help to make Winter feel a little bit cozier.
Source: Flickr User Maricel Cruz