King of sedan

purchased this in april 2017 most spacious more stylish and can say king of sedan, but the milage is not good as of now. Sun roof adds the look for city. The interiors are so cool with smooth touch. Till date I have done with 2 free service but in high way I can make out 18 to 20 milage km but in city limits it has been reduced to 13km so kindly make the major point and work on it for better milage