Our Natural resource   like petrol or diesel are so precious to us .so don't misuse the resources even its price may decrease..To conserve the petrol or diesel we  can keep these points in our mind.
The first  one is to keep or maintain the vehicle in good condition  which means,according to the terms specified you have to service  the vehicle correctly and change engine oil,oil filter periodically.
IF the engine becomes hot ,don't  start the vehicle and use it for long time.
When you are in traffic signals and even in railway cross please off the vehicle . It helps to conserve or save the petrol. If tyre doesn't have enough air, please check the pumps and if it is need
Pls fill the air. Otherwise it will affect  the milage. Use AC  only if it is needed . If we on the AC Fulltime,10%or15% the milage will decrease.When you increase the speed of the vehicle you can  use the  AC,it will help to save petrol. Because, when the vehicle run so fast at that time if the window is opened, we need more energy to burn to prevent the air. Most of the people think that they should drive the vehicle in topgear then only they can save petrol. This thought is  such utter nonsense . And also most of the people have a habit that when they start to drive, they change the gear to  top gear not even covering 10km.  Every one should remember that according to speed of the vehicle  and situations,, the gear should be changed.then only they will  get maximum milage. When the RPM become 2000-2500 at this limit only you can use  the top gear . When you are in 30km/hr you can use the third gear. And when you are in 40km and 50km you can use 4th &5th gear. Like this you can change gears. The details of gear changing , you can go through  in the  service book.  Avoid over speed . In an hour 45-55km speed gives more milage when the90km covers  you need 15%extra petrol. Park your vehicle in shade area or in cool place. This helps to reduce vapourising the petrol.