Replace the regular incandescent light bulbs with compact fluorescent light bulbs (cfl).
Clean or replace air filters on your air conditioners.
Use less hot water (in the shower or for washing clothes).
Use a clothesline instead of a dryer whenever possible like in summer & winter.
Turn off electronic devices like TV, computer, DVD player when you're not using them.
Unplug electronics from the wall when you're not using them cauz things like hairdryers, TV & cellphone chargers use energy even when turned off.
If you got a watch or a cellphone, don't buy display clocks for your house.
Buy recycled paper products.
Plant lots of trees.
Buy fresh foods instead of frozen.
Avoid heavily packaged products to cut down on your garbage.
Reduce the no. of miles you drive by walking, biking, carpooling or using public transport.
If u have a car, maintain it properly to improve fuel efficiency & reduce emissions.
Check your tires weekly to make sure they're properly inflated.
PS: Don't question this just do it. Watch David Attenborough's State of the Planet & also watch Al Gore's An Inconvenient Truth.