Step 1: Have or consider buying a high mpg car
If you have a high mpg vehicle (we're talking over 30 mpg here) and you use it as your regular car, go ahead and check all the next steps off, you're done. If not, but you're considering buying one, move on to step 2. As an aside, if you absolutely need a big truck, you can substitute a biodiesel vehicle run on waste grease for a high mpg car.