I have Jawa 42 BS6 and I had done my first services but my Jawa bike is giving 26.7 average how I can increase that?

I have jawa classic, now its run 798 km and i hv purchased on 21 oct 2021. First service not complete.First i fill 10 Ltr average mileage got 25.52km/ltrSecond i fill 4 Ltrs average mileage got 28.31km/ltrThird i fill 4 Ltrs average mileage got 36.76km/ ltrFourth i fill 3 Ltrs but till date no reserve signal found.Total KM run till 10/111/2021 798kmTotal filled fuel 21LtrsMileage average - 798/21=38Km/ltr

In order to get better fuel efficiency returns from your bike, there are some points that you can keep in mind while riding such as keeping a check on tyre air pressure, timely service your bike, maintain proper gear to RPM ratio, do not accelerate the bike unnecessarily, ride your bike at economical speeds, etc.