Cars Q&A

Gd mrng sir, I am learning to drive a car. Every one says that to get maximum mileage I have to try driving at a constant speed as more changing gears & applying clutch may reduce mileage. I have new i10 VTVT engine car & according to them 4 valves playing same at constant speed demanding low petrol while changing in gears its uses of petrol got higher. Are they right? Suggest me you. . . how to drive efficiently.