A Bright Idea - Turning out lights when you leave the room is an easy way to save electricity. If you have a problem area like a hallway or closet consider switching out your light fixture for one with a built in motion sensor.
Chill Out in Your Room - Check windows, doors and switch plates to make sure they aren't leaking cool air. Weather striping and plate insulators are available at Home Depot. For windows that let in just a bit too much heat add heavy drapery to block the sun. If you still want the light but not the radiant heat then consider installing a radiant film on your windows. They can block as much as 70% of the sun's radiant heat in the summer time. This is also available at Home Depot.
Look into carbon free ways to generate and save electricity in your home. Consider installing a solar hot water heater or solar panel, use you bike to get to the store, car pool when possible, combine errands to save on gas, etc.