Brothers, dont be sad about not getting a fuel average display in the speedo. An accurate method is to get the car filled and ask the boy to stop when the pump stops automatically (don't let him manually put small squirts). This car has 2 trip metres. Reset one of them.
Drive around for a while and then get the car filled again (again till the pump stops automatically). Divide the reading on the trip metre with litres of fuel. You will get an accurate average.
Illustration:
distance travelled: 100 km
Fuel filled: 10 ltrs
Calculation: 100/10 = 10 km/ litre
I have an avg calculator in my corolla and the reading is always the same as the above manual calculation (except for a few decimal points, which is negligible)
Note: don't let the pump guy round the amount to 100s etc. I always step outside the car while it is being filled - a small hassle to satisfy the keerra for calculation :p.
The good thing about having 2 trip metres is that you can use trip A for mileage calculation and trip B for oil change calculation (there is no trip B metre in honda city btw, so another alhamdolillah).
For mileage, I have found PSO pumps not satisfactory (my office has arrangement with PSO cavalry and ghazi chowk and my corolla's engine does severe knocking on their fuel. I had a city from 2010 to 2012 and it's knocking was worse on PSO). I recommend shell, model town morr, followed by shelll, liberty, followed by total, MM alam, opposite freddy's.
A good way to improve mileage is to avoid immediate acceleration and hard braking; and to drive the car between 2k and 3k rpm. However, a lot depends on how many stops or trips you make in a day. So if a colleague on the same car who just comes from defence to gulberg and goes back in the evening gets 15km/litre, but you have to make visits during the day also, you may get 12 km/litre on a similar engine.
Another tip is to get to fuel filled when the tank reaches half as petrol evaporates quicker when there is more space (you would also notice that the second half of the tank gets consumed quicker than the former).
As suggested above also, dont let the pump guy put squirts manually after the pump trips automatically. I understand that the new pumps have a return line right below the pouring nozzle, to cater for overflow, so some of the squirts actually go back to the pump on ur expense. So it is always better to step outside and ask the pump guy ke barri mehrbani, efficiency mat dikhao aur meri calculation mat kharaab karo 
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