Importance order is in Descending

Mathematics - Differential and Integral calculus, coordinate geometry, 3D geometry,probability, Trigonometry, Matrix and determinants.

Physics - Mechanics, Electrodynamics, Heat and Thermodynamics, Modern physics, SHM and Waves and Optics.

Chemistry

Inorganic - Chemical bonding, S-block, Periodic table and periodicity properties.

Physical - Atomic structure, Ionic equilibrium, Nuclear chemistry, Mole concept, Thermodynamics and Thermo chemistry, Chemical kinetics, Electro chemistry, solid state, solution and colligative properties, surface chemistry (all are equally important)

Organic - Alkyl hallide, Alcohol and ether (reaction mechanism), Aromatic compounds, biomolecules, carbohydrates, amino acids, polymers, carbony compounds, environmental chemistry, grignard reagent, reduction,oxidation and Hydrolysis.

Study in descending order to score maximum.

Refer https://admission.aglasem.com/most-important-chapters-jee-main/ for more Information.

All the best!

Note that JEE Main almost asks questions from each and every topic, But there are some chapter which dominates over other You can expect questions from this topics

Physics: Rotational Motion, Optics, Thermodynamics, Electrostatics.

Chemistry:Chemical Bonding, Equilibrium, p block elements, Kinetics, Aldehyde, ketones and alcohols.

Mathematics: Calculus, Coordinate Geometry, Quadratic Equations.

Important topics for physics

Wave optics, heat and thermodynamics, electromagnetic waves ,semiconductors, Ray optics, gravitation, Photoelectric effect oscillation.

Important topics for chemistry.

Atomic structure electrochemistry nuclear , surface chemistry, aromatic compounds, alkyl halide ,chemical bonding ,chemical kinetics coordination compounds.

Important topics in maths

Vector 3D ,geometry ,determinant and matrix probability ,circle ,straight line, sequence and series.