Dear Pratik,

You can consider below tips -
Complete syllabus as it requires to devote 10-12hrs in a day.
Once you clear the syllabus and all yur concepts are clear then you will have to give more attention for important topics of ISI Admission Test Indian Statistical Institute. It would be better if you make the notes of important topics and revise them all regularly.
For better preparation you have to solve the previous year question papers of ISI Admission Test or you can buy books for it -
Best books for preparation :
MECHANICS
H.C. Verma
Resnick and Halliday
I.E. Irodov
OPTICS
H.C. Verma
HEAT AND WAVES
H.C. Verma
Resnick and Halliday
ELECRICITY AND MAGNETISM
Resnick and Halliday
R.J. Smith  Circuits devices and systems
I.E. Irodov
MODERN PHYSICS
H.C. Verma
I.E. Irodov
Chemistry:
GENERAL CHEMISTRY
J.D. Lee