There are little things that should be kept in the mind and after that automatically you'll notice that your scooter is performing better in the same quantity of fuel. Although, you can't increase the mileage of the scooter from the value declared by the manufacturer but you can try and achieve that.
Few Things that should be kept in mind:-
1. Get your scooter serviced at the appropriate interval. The interval or the time your scooter needs servicing is mentioned in the user manual.
2. Read the full user manual carefully, this will make you aware of tips and manufacturer recommendations.
3. Always have the air pressure of the tyres under check as tyres with more or less pressure that normal affect mileage.
4. Always refuel your scooter from that petrol pump that provides you good quality petrol.
5. If you can afford premium petrol then go for it and you'll automatically notice the difference.
6. Don't ride your scooter fast. Try to manage a constant speed between 40-60 Km/h. The more you'll rev the accelerator, the more fuel it will consume.
7. Try to use brakes only at the appropriate time while driving. Let the brakes free if you're driving in a traffic-free road.