Hello,

Your basics in Physics, Chemistry & Mathematics should be very clear upto 12th std, you should read NCERT books of Physics, Chemistry & Mathematics of class 11th & 12th at least 2 or 3 times for basics. After that HC Verma for Physics, RD Sharma for Mathematics, OP Tendon for Physical & Inorganic Chemistry, and Organic Chemistry of "Arihant Publication" for detail or extra knowledge. 

You should also try to solve the previous years question papers, this helps too much and you should also give the mock test to rectify yourself and build your confidence level.

For preparation of exam, the most important thing is your confidence after that you should know the whole syllabus and make your plan properly for learning new chapters, solving the numericals and revision. All three things should be the part of your preparation strategy in daily routine.

Thanks for query

All the best

NCERTbooks are strongly recommended alongside following books as per toppers and experts:

• Physics by IE Irodov and HC verma
• Chemistry by OPTandon 
• Mathematics by RD Sharma. 

All these are most renowned books. Students also recommended to solve all previous year papers and analyse trend and mistakes.