Here are some basic car maintenance tips to save gas.

1. A faulty oxygen sensor can be very bad. Replacing it can improve your mileage up to 40 percent.
2. Replacing a clogged air filter can save up to 10 percent. It also protects your engine from contamination and long term damage.
3. Replace spark plugs every 60-90K miles. Spark plugs get weaker over time. An improperly firing spark plug will decrease engine performance. Platinum plugs are usually only a few bucks more too.
4. Don’t speed. I don’t like this one either, but it does help. Note that best gas mileage is not low speeds but usually around 50-60mph when you transmission gets into top gear.
5. Easy on the brakes. Don’t speed up to stop. If you are coming to a stop, take your foot off the gas earlier. Using brakes equals bad gas mileage.
6. Overuse of AC compressor. A/c does not really take that much to run, but having cranked to max all the time will hurt a bit. Try a lower setting.
7. Lose gas gaps. Takes less than a second to check the cap each time.
8. Keep Tires Properly Inflated. You can improve your gas mileage by around 3.3 percent by keeping your tires inflated to the proper pressure
9. Dirty or wrong engine oil. Do not used unsealed or unknown oil. Go with a Valvoline, Castol, Penzoil, etc, etc. Also be sure to use the exact oil. Using the wrong oil can take a few MPG off your trip.