50 km/litre mileage in my Yamaha FZ (153cc)

It is being 1 year I am riding Yamaha FZ 153cc bike. Till first service, from the Yamaha's authorised service centre it had around 48 kmpl mileage. Then it gone down to around 30 kmpl for the following 1 - 2 months. But I managed to increase it with economy level riding. I always try to manage the bike's speed between 40 - 50 kmph. It is not possible to maintain the same speed because of the traffic in town area. But because of perfect level of riding it then managed to give around 35 - 40 kmpl.