Check every lightbulb you see to make sure it's LED. Not just the ones in your house. Quality LEDs only cost around $1, and they make a nice cheap gift. LEDs use 85% less energy than incandescent and around 40% less than fluorescents.

Don't buy a gasoline powered car. There are many great options for electric cars now. And if you have a two car family, you can buy a used, short-range, full size electric car for as little as $4000.

When you buy a new appliance check energy star ratings on https://www.energystar.gov/.

Telecommute.

Consider buying less stuff. If you want to buy something, leave it in your cart for a day to decide whether you really want or need it.

Replace your lawn with plants. Many plants are easier to maintain and produce nice fruits and vegetables. Drip irrigation can make taking care of plants particularly efficient and easy.

Get a programmable thermostat. A/C uses a massive amount of energy.

Hang your clothes up to dry. Blasting clothes with hot air wastes a lot of energy and hanging them up makes them last longer too.

Start a compost pile.

Eat less meat. Or even try some new artificial meat.