Quick wins: replace all your incandescent light bulbs with energy-efficient fluorescent bulbs (although you can't do that if your bulb is on a dimmer, sadly); use Energy Star appliances; turn off and unplug any unnecessary devices, including those "wall wart" power adapters; make sure your home is insulated from top to bottom; get an energy audit from a local contractor to see if your house is leaking heat (or letting heat in when your AC is running); replace all weather striping on your doors and windows to prevent drafts; install rain gutters and a rainwater reclamation tank in your basement and use that water for your lawns; use reclaimed or renewable materials for any home improvement projects (e.g. used hardwood floors, or countertops made out of a mix of recycled glass particles, which can look beautiful, etc.); use low volatile organic compound (VOC) paint.
Longer-term fixes include installing wind turbines and solar panels on your property.
This Old House magazine had an interesting, very detailed series about a full-blown green restoration project (link below). I hope this helps.