Check air filter, it must be clean. Replace if extremely dirty.
Use 0w-20, 5w-20 or at max. 5w-30 Fully synthetic engine oil from some reputed brand. If you want best for bucks, go for ZIC or Total Quartz 9000 Future series, and change along with genuine oil filter after every 5,000 Kms.
Reset trip meter(s), and start measuring fuel efficiency.
Drive with extremely light foot / soft pedal. Do not accelerate / decelerate suddenly. Apply brakes gently.
Keep proper Tire Pressure as suggested by the OEM. Do not follow 28 psi or 30 psi myth, or hot summers, etc.
Get wheel balancing & alignment done, at least for once.
Use Fuel by Shell or Total only, and preferably from their company operated / maintained fuel stations.
It may not be the problem specific with your car. Usually, AC of 660 cc cars haven't been found impressive IMO. Still, you can get the AC system, especially the gas checked, for any leakage or under-fill, etc.
For garages in Lahore, fellow members from Lahore can guide better.
I hope, it helps. Thank you.