Well it very much depends on where you live.
I use Hi-octane(why, I have my reason), 33 psi tire pressure(top-up every week).
A lot of folks dont understand this and i will not explain myself.
For preventive maintenance after every 5000km's, based on availability, I use Liqui moly Fuel system cleaner or Valve cleaner .
During first 8000km i used Liqui moly Cera Tec and during brake-in phase that's initial 1500km, I drove it with only 1 passenger again, I have my reasons.
In 1 year and 5 months i have driven it 16000km's.
Within City it gives me 15km per liter
Islamabad highway it gives me 20km per liter at speed of 80km an hour.
On Motorway drove it between 100km to 110km and it gave me 18 to 20 km liter. Travelled twice on it from Isloo to Sialkot via motor-way and it ate 25 liters and covered 488 kilometers.
Isoo to Harnoi via Motorway the average was 19 km per liter.
And Isloo to Hunza it was between 16 liters per liter, High Octane is not available over there and fuel quality is highly questionable.
Once you reach 120km you can feel the drag on the car, its super happy between 100 to 110 .
All of above calculations are tank to tank.
In Bumper to Bumper traffic average is really poor. With AC its gives me 13.5 to 14.