Get it serviced from 3s dealer including throttle body cleaning, tappets adjustment and get it's spark plugs checked. Last but not least, Change Air filter and stick to Genuine Honda product. Never ever go for leppon/Guard filters as they are piece of crap right out of the box. Try to get fuel from a reputable station and mix Hi-octane in 60:40 ratio for 5-6 fill ups. Stop using 10w-30 oil and switch to synthetic 5w-30/5w-40 along with genuine oil filter. Also get your car's rims and tires properly balanced. Balancing plays a very important role in mileage. Sadly people here don't give a damn about it. You will notice improved mileage for sure.
Mine of easily does 15km/l on long with AC and 12-13 km/l in city driving without AC with normal + hard foot.