Keep your vehicles tuned and in good mechanical condition. Keep your filters and fluids cleaned. Use high-efficiency motor oil. When buying a new car, consider getting a model with 35mpg or more. Keep tires properly inflated.
Low pressure reduces gas mileage and the life of the tire.
Avoid using drive-thru windows. Park and go inside instead. Do errands on the way home from work, and consolidate trips when you have to drive. This releases gas vapors and often results in spilled gasoline which leads to ozone formation.