Get the car be scanned with a diagnostic computer and watch the live data. There are three parameters which reveals the fuel mileage.
1. Air fuel ration sensor. It should cycle two to three times per second.
2. Short term fuel trim. It should read +- less than 10%. It is considered best if it is as close as to 0% at idle speed at operating temperature..
3. Long term fuel trim. It should also read +- less than 10%. It is considered best if it is as close as to 0% at idle speed at operating temperature...
If the live data is according to the above mentioned values, it is OK. Just drive it, let it to bed in completely up to 5000 Km.
After the completion of 5000 Km get it properly tuned and calibrated with the diagnostic computer.
When ever you find a free space, or down steep, release the accelerator pedal (Do not neutral the car) and let the car roll in top gear as much as the speed remains within the top gear so that you could accelerate and decelerate it again.
NOTE: This tip is not applicable within the city drive but on Highways and the Motorway.