Tips to follow to improve mileage!
~ Clean and correctly adjust the spark plug.
~ Change the spark plug if necessary.
~ Use tubeless tyres.
~ Use recommended tyre air pressure (depends on tyres).
~ Make your air/fuel mixture lean till some extent. Don't make it too lean as it would give birth to starting problems!!
~ Change the engine oil , gear oil.
~ Change\Clean the air filter depending on the Kms run.
~ Check free movement of brake liners.
~ Fill fuel from reputed petrol bunks like Shell, etc.
~ If battery died, Replace it.
~ Try to avoid unnecessary brakes and hard acceleration.
~ Last but not the Least, Maintain the Speed between 40-50 Km/h.
See this link too. It was prepared for all two wheelers but it can be useful too!
Link: Click Here