Is average of a car is increases after first servicing?

My car is new honda city VXI

Yes, the engine gets free after 1st service and will give a bit more mileage.

But remember that it is best dependent on how you drive the car. Don't run ac all the way, turn off when not in need, don't accelerate unnecessarily, better to turn ac off in traffic, keep slight foot on clutch so that it not pressed at all times, put car to neutral when you feel acceleration is not required like going down the hill or slopes and manage only through braking, never turn the keys off or remove while driving, wear seat belt always.