In order to prepare for JEE make sure your basics are clear.  You can take help of NCERT books. After, that you can refer other recommended books.

If you want you can also join crash course for your preparation.

Solve previous year papers to understand the exam pattern and level of questions. You should also solve mock test series to analyse your preparation level at regular interval of time and to know your strength and weakness. So, you can work accordingly.

Work on your time management as well to increase your speed and accuracy.

You should focus on the topics which carries more weightage in the exam. Solve MCQs related to it for your practice.

You can check the important topics below which carries more weightage in the exam

Physics

Capacitance- 6.67%

Current Electricity- 10.00%

Calorimetry & Thermal Expansion- 6.67%

KTG & Thermodynamics- 6.67%

Rigid Body Dynamics- 6.67%

Work, Power & Energy- 6.67%

Modern Physics- 10.00%

Chemistry

Chemical Bonding- 6.67%

S-Block- 6.67%

Alkyl Hallide, Alcohol & Ether (Reaction Mechanism)- 13.33%

Mole Concept- 10.00%

Mathematics

Co-ordinate Geometry (3-D)- 6.67%

Application of Derivatives- 6.67%

Functions- 6.67%

Matrix & Determinants- 6.67%

Probability- 6.67%

Good Luck!!