If you're using incandescent bulbs, think about replacing your on/off switches with dimmers. (Special dimmers are available for fluorescent bulbs and low voltage halogens - be sure to get the right dimmers for the bulbs.) Dimmers give you more control over lighting levels, and when you dim the lights, you use less energy. If you find that you're always dimming the lights, maybe you should replace your bulbs with lower wattages.