Not only does slowing down and observing the 55 mph speed limit help maximize fuel efficiency over speeding at 60, 65, 75 or even more mph, but checking the air in your tires and the air filter in your car are useful as well.
I check the air in my tires at least once a month. Knowing your number, in my case, 32psi, along with owning a tire pressure gauge and knowing which gas stations have free air (Amoco or PDQ in my area) helps keep me well inflated. I usually find at least one tire low so I fill it up and am ready to go.
Also, I cannot argue with the air filter advice. I had my oil changed at one of those quick oil changing places over a year ago, and they showed me my air filter. It was filthy so I agreed to have them change it. My next fill up, my gas mileage increased by over 2 miles per gallon. That is impressive!
Not only do these actions maintain peak fuel efficiency, but they also keep your car in shape for the long haul. Just stop at a gas station in the morning before work, check the air pressure and add air if needed. Most experts recommend checking air pressure when the tire is cold, not warm from miles of driving.
Get to know where your local auto parts stores are. Stop by and pick up a new air filter or ask to have your trusted mechanic replace it during an oil change. Some of the auto parts store employees might even replace your filter for you. They replaced my windshield wiper blades when I purchased new ones. And while you are picking up a new air filter, ask the nice gentlemen where the tire pressure gauges are and pick up one for your use. That small purchase will pay you back quickly with peak fuel efficiency.