To score good marks in physics you should work on your basics make your concepts strong. You can follow NCERT book for your preparation. Refer previous year questions to understand the level of the questions asked in the exam. 

You can check the important chapters of Physics below which carries more weightage in the exam

JEE Main

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%

BITSAT

Heat & thermodynamics- 10%
Magnetic effect of current & magnetism- 9%
Current electricity- 6%
Electrosatatic- 5%
Wave motion- 6%
Simple harmonic motion- 5%
Wave optics- 5%
Ray optics 45
Work energy power- 4%
Rotational motion- 4%
Elasticity- 4%
Fluid- 4%

Good luck!!