If you are preparing for JEE Main below are the topics in which you should focus more as they carry more weightage in the exam.
You should read NCERT books completely as syllabus is based on them and you can also get direct questions from NCERT books.

Mathematics-

Coordinate Geometry
Continuity/ Differentiability, Limits
Complex No., Quadratic equation
Integral Calculus
Sequence and Series
Trigonometry

Physics-

Current Electricity
Electrostatics
Optics
Heat and Thermodynamics
Law of Motion
Waves
Simple Harmonic Motion

Chemistry-

Transition Element and Coordination Chemistry
Periodic Table and Representative Elements
Gaseous State
Atomic structure
Amines
Solution and Colligative Properties
General Organic Chemistry
Carboxylic Acids and Derivatives
Hydrocarbons
Carbohydrate, Amino Acids and Polymer

All the Best!!