Step 1 : Increase the surface area with the road
Always inflate the tires with the recommended pressure prescribed by the manufacturer as under-inflated ones increase the surface area with the road, which in result makes the engine do more.
Step 2 : If you’ll drive in a fuel-efficient mode
It would be more mileage giving if you’ll drive in a fuel-efficient mode—driving between 60-80 km/h—no throttle inputs and put brake softly.
Step 3 : Donot overload your car
Try to keep your car light-weighted
Step 4 : Use AC smartly
Keep AC off when the weather is tolerable, but you can turn it on & windows up on the highway because it reduces aerodynamic drag.
Step 5 : Fill the gas tank in the morning
Refill the gas tank in the morning as the temperature is lower—the volume of gas decreases—it becomes dense, and you will get more fuel in the same amount.
Step 6 : Service your vehicle time to time
Service your vehicle time to time and use recommended oil & additives as per need.