Replace incandescent lamps, (ie. regular light bulbs) with compact fluorescent lights. While more expensive to purchase, (prices continue to drop and they are now under $5 each in packages of 3 or 4 lamps) they pay for themselves with time, taking 1/4 of the power and having a life of 7 to 10 times a long. They also generate much less heat which is a big bonus during the summer. You will get full life expectancy out of these lamps in open fixtures where the air can circulate and you will get a shorter life in a fully enclosed light fixture due to somewhat higher temperatures lowering the life of the internal electronic circuitry.