Hello shibu,
Good day to you !!
Being a first time driver after owning a car, these are the certain aspects which i understood / follow to reap better mileage (especially in Zest):
1) Shift to top gear (5) as soon as possible, even if you have not reached the specified rpm levels as directed in user manual
2) Do not press the accelerator hard when cruising at speeds of 80 ~ 100 Kms (around 2k rpm). Just have a light foot on accelerator, which will ensure that you are always past the 15 Kmpl mark on fuel gauge display.
3) Instead of applying sudden brakes, release / take off your foot off the accelerator if u foresee a traffic or man movement
4) Reduce sudden downshifts.
5) You have better chances of getting mileage (atleast above 20kmpl) when you fill the fuel and cruise in an highway, which may get compensated during drive in city traffic.
I have made about 5 trips from Chennai to Coimbatore (2) and Bangalore (2) and Hosur (1). The mileage during these trips would average between 22 ~ 25 Kmpl.
Please remember, i'm not an expert. Just passionate on driving
Try some of these, and do revert if you can find any improvement. Ofcourse, your vehicle being an AMT, not sure on the application of all the above points. May be seek some advice from TAI experts.