Bro there is no need to worry
if u want best fuel average then 1st of all u check these things
1) use ZR or HR tires in your car not ordinary radial tyres
only ZR or HR high speed raidial tyres recommended
2) only use hi octane
3) drive under 60 speed
4) 0 W 20 engine oil
beside these there are several condition which also effect fuel average
1) wind pressure
2) slopy roads
3) tyre air pressure
so enjoy your ride and be safe
i have prius G 2014 top of the line variant
i use 205/45ZR17 tire Maxxis brand
it gives me 29Km/L in winter
and in summer it gives me 33km/ltr