Combining errands into one trip saves you time and money. Your fuel economy is worse when your engine is cold than when it is warmed up. So, several short trips taken from a cold start can use twice as much fuel as a longer, multipurpose trip covering the same distance.
Trip planning can reduce the amount of time you drive with a cold engine. It can also reduce the distance you travel.
Stagger your work hours to avoid peak rush hours.
Drive your most fuel-efficient vehicle.
Consider telecommuting (working from home) if your employer permits it.
Take advantage of carpools and ride-share programs. You can cut your weekly fuel costs in half and save wear on your car if you take turns driving with others. Many urban areas allow vehicles with multiple passengers to use High Occupancy Vehicle (HOV) lanes. HOV lanes are typically less congested, further improving your fuel economy.
Consider using public transit if it is available and convenient for you. The American Public Transit Transportation Association has links to information about public transportation in your state.
Source: United States Environmental Protection Agency: www.fueleconomy.gov