Old tires lose their traction on the road eventually, and they have to spin more to maintain a certain speed. This consumes more fuel than necessary. Low tire pressure can also lead to more fuel consumption. Do check your tires air pressure in regular intervals. Keep your tires at an optimal pressure as recommended by the manufacturer. Wheel alignment must also be right to get the best fuel economy for your car. Tires in good condition also improve the handling of your car. 
Poor Fuel Quality

Poor Maintenance
Delayed and poor tuning of your car can lead to higher fuel consumption. Make sure your mechanic is skilled or take your car to a dealership certified by your car’s manufacturer. Company dealerships usually have the right tools and machinery to take good care of your car. However, they charge more than local vendors. Keep a schedule chart in your car’s dashboard to note down car tuning dates. This will help you get your car’s tuning and servicing done on time. 

Over-speeding, Overloading and Air Conditioning
Over-speeding always puts a strain on the engine as it has to work hard. This results in more fuel consumption than driving at normal speeds. Generally, in normal cars, speeds above 120 km/h result in fuel wastage. Similarly, overloading also puts undue pressure on the engine. In order to propel the added weight, the engine must work harder to produce more power; therefore, using more fuel in the process. If you are driving with air conditioning turned on, the engine surely consumes more fuel.


Reference:
Pakwheels.com