Set your tires to the proper inflation. Properly inflated tires can reduce fuel consumption by up to 3%. Your tires also lose about 1 PSI per month, and when the tires are cold (e.g., in the winter), their pressure will decrease due to the thermal contraction of the air. It is recommended to check tires at least monthly, preferably weekly. Having properly inflated tires will also help you avoid uneven wear on the tread.
When getting your oil changed, use a synthetic oil additive to either natural or synthetic oil. This can increase your gas mileage by up to 15% if you follow the manufacturer's instructions and recommended usage.
Get your car's window tinted. Hotter times of the day when the sun shines brightly a cars interior can benefit a great deal from window tinting. The less direct sunlight that gets into the car,less time cooling off the car. This helps you get better gas mileage on your vehicle. If the car is cooler when you enter it, it takes less air conditioning to cool it off.

 

buy a scan gauge and pay attention to the numbers.