*This is suggested to use some other reference books along with NCERT Books .However, NCERT books are the most preferred for national level competitive exams as these books comprise of topics in easy language which helps to grasp them well.

*But reference books are useful for practicing with various questions related to a topic. So, you should use some reference books and solve previous years KVPY question papers to prepare well.

* And if your target is 90+, I would firstly suggest you to practice previous year question for JEE. Generally physics and chemistry are not so much tough but mathematics is. Chemistry questions mostly comes from NCERT dont worry if you have a clean and clear concept about that,

*Try to score as much possible in the 1 mark problems and then for the 2 marks, choose physics and chemistry unless you are too much confident in maths.

*The main work you need to do, to maximising your score is the time management. And ensure that by the time you appear for the exam you have finished the entire JEE syallabus . Don't worry questions will not be as tough as JEE advance.

Hope it helpful