if you are using your car on petrol , here are some amazing tips which are applicable in Pakistan only (I guess):-
1- Generally Caltax and Shell fuel is good, but not in every case. Try to fill almost half tank from different station and check the consumption. It will differ for all pumps, so note down the pump which gives you best, 2nd best and 3rd best mileage and only fill from them.
2- Fill your tank till 'dhakkan' and top up frequently (500 , 1000 ka fuel khatam ho jayee to dobara top kerwaoo). This will make sure that fuel pump is not making any 'dandi', because you can see the fuel.
Also here are some other tips:-
1- Always fill your fuel in nights and not in hot sunny days.
All above tips are apart from the fact that you have done proper tuning, all the filters and all the fluids of your car.