You may not be able to reduce global warming, end pollution and save endangered species single-handed, but by choosing to live an earth-friendly lifestyle you can do a lot every day to help achieve those goals.
The single most import thing you can do to for the environment is to leave your car at home. Every time you do you reduce air pollution, lower greenhouse gas emissions, improve your health and save money. Walk or ride a bicycle for short trips, or take public transportation for longer ones. Research has shown that people who use public transportation are healthier than those who do not, and families that use public transportation can save enough money annually to cover their food costs for the year.
When you do drive, take the few minutes needed to make sure your engine is well maintained and your tires properly inflated. Every little bit helps.