Throttle body cleaning, O2 sensor check, air filter, Use 0w-20 engine oil, tyre pressure 36-34, always drive in D and not in S or B, don't exceed the accelation limit and be in the Eco mode... You will experience a maximum of 14kmpl, and in city 11-12... That the best this car can give...
BTW what does that mean: "it's decreasing rapidly and increasing very slowly"