What are the main topics i should be concentrating on from all the 3 subects ( PCM) to be able to qualify jee mains entrance? Please advise.

Physics:-
Electrostatics & Gravitation(conceptually similar)
Current Electricity &Heat Transfer (conceptually similar)
ElectromagneticInduction
Waves (Sound as well as optics)
GeometricalOptics
Thermodynamics and KTG
Rotational Dynamics

Chemistry :-
Chemical Bonding & the periodic table (Basic for all other chapters likeCoordination Compounds and prediction of properties ranging from MP,BP, Solubility to reactivity, optical rotation etc.
Carbonyl Compounds & their derivatives
Redox reactions, Mole Concept & the concept of equivalents
Solid state, solutions & gases theory
Thermochemistry & the Second Law of Thermodynamics

Maths :-
Matrices and Determinants
Definite Integration
Vectors and 3D
Differential Equations
Conic Sections and Straight Lines
Basic Equation Solving(Trigonometric, Quadratic, Bi-quadratic)
Sequences and Series
Formulas of a triangle

Physics
Dimensional Analysis – Although a very easy chapter but knowing correct units and dimensions for physical quantities can easily help you to eliminate options in multiple choice type of questions
Gravitation &Electrostatics – Thesechapters are conceptually similar to each other(in terms of attractive forces concepts)
Current Electricity &Heat Transfer – again these are conceptually similar to each other. So, when you read these chapter watch out for the similarities (which might be deceiving at times)
Electromagnetic Induction,Waves & Sound
Geometrical Optics ,Thermodynamics
Kinetic Theory of Gases,Rotational Dynamic