Walk or Bike When Possible
If you can, choose walking or biking instead of driving. Leave your car in your garage, and grab a stroller or your bike to visit the post office or grocery store. It is a great way to get some exercise, spend time alone with your child, and save extra money, too!
Don't forget public transportation! While bus, subway, or train fares may sometimes seem steep, don't forget that driving your car involves more than the price of gas: There's wear and tear, parking fees and worries, risk of accident, and not least, the environmental impact.
Modify Your Driving Style
This has the promise for being the most rewarding in terms of gas savings, but may be the hardest to implement. Driving more slowly, less aggressively, and more mindfully will significantly improve your miles per gallon. This is true generally but is magnified at highway speeds.
The government website Fueleconomy.gov says that each five miles per hour you drive over 60 mph is like paying an additional $0.30 per gallon for gas. Tom and Ray Magliozzi (a.k.a. Click and Clack, or The Car Guys) of the radio program Car Talk say, "Slow down. You'll be a safer, more relaxed driver, and you'll increase your fuel efficiency. And, believe it or not, due to an unexplained Einsteinian time warp, you'll also get to your destination in about the same time."
Rapid acceleration and sudden braking are big eaters of gas. Don't zoom up to the stop sign, screech to a halt, then peel out on your way to story time at the library. It's just not worth it. We'll forgive your driver if you're in labor and on the way to the hospital, however.
If your car is going to be stopped for more than a minute, turn it off. When you are idling you are getting zero miles per gallon.
If you drive a vehicle with a manual transmission (i.e., stick shift), shift into higher gear as soon as is reasonable. When running in the lower end of a gear, the engine turns more slowly and saves fuel.
Finally (and feel free to share this with your spouse), don't be too proud to stop and ask for directions. It's a lot cheaper than burning gas driving around lost.