Don't warm up your car before driving - that is one of the biggest reasons for your high fuel consumption. Just start, put it in gear, and drive off gently. Keep the rpm low on a cold engine - generally not more than 3k at max (preferably less than 2k).
When anticipating a stop, or a checkpost, stop accelerating. Bleed your speed gradually in gear before braking.
Drive at just enough speed to keep up with traffic - your average speed will hardly vary in city driving in most situations.
Oh, and 22 kml is a piece of cake for a Honda City. You don't need to drive on the highway to achieve that - with the right knowledge and enough practice you can actually exceed that in city driving.