Use low wattage light bulbs. Use fluorescent bulbs instead of incandescent. Keep your lamps and fixtures clean. Dirt inhibits light reflection. Use light wall colour.
Dark colours absorb light, while light colours reflect it.
Put your lamps in the corner of the room. Light reflects better against two walls than in the centre of the room. The Alliance to Save Energy has more great tips on how to be more energy efficient. Close the vents in unoccupied rooms. Close the fireplace flue to prevent heat from escaping up the chimney.