Replace your light bulbs with CFL's

This one is preached to death for a reason: It's an easy one everyone can do. While compact fluorescents are initially more expensive than the incandescent bulbs most people use, they last 10 times as long. What's more, a compact fluorescent will lower your energy bills by about $15 a year, and by more than $60 during its life. It will also keep half a ton of carbon dioxide out of the air.