Hello aspirant

As Jee main exams are conducted after xii board exams, you already have enough knowledge through STD xi and xii board syllabus. Get clear concepts about every topic . As Jee syllabus is also completed during xi and xii  . So when you are doing your board portion after each chapter go on solving Jee MCQs topic wise. Whatever topics are included in syllabus do them with  perfection.

Hi

If you are preparing for JEE mains then you should stick to syllabus provided by NTA as it is theconducting body for JEE Mains examination and questions will be from the syllabus only so you don't need to study topics which are not included in your syllabus , what you should do is master the concepts which are there in your syllabus, practice numericals and MCQs from the chapters which are there in the syllabus so can perform well in your JEE Mains examination.

JEE mains syllabus by nta for each of Physics, Chemistry and Mathematics is provided below:-

PHYSICS:-

Physics and measurement
Rotational motion
Thermodynamics
Gravitation
Laws of motion
Oscillations and waves
Kinematics
Work, energy and power
Properties of solids and liquids
Electronic devices
Kinetic theory of gases
Current electricity
Communication systems
Electromagnetic induction and alternating currents
Magnetic effects of current and magnetism
Optics
Electromagnetic waves
Atoms and nuclei
Electrostatics
Dual nature of matter and radiation

CHEMISTRY:-

Some basic concepts in chemistry
States of matter
Atomic structure
Chemical bonding and molecular structure
Chemical thermodynamics
Hydrocarbons
Chemistry in everyday life
Principles related to practical chemistry
Organic compounds containing halogens
Organic compounds containing oxygen
Solutions
Equilibrium
Redox reactions and electrochemistry
Chemical kinetics
Surface chemistry
Purification and characterisation of organic compounds
Organic compounds containing nitrogen
Polymers
Some basic principles of organic chemistry
Biomolecules
Classification of elements and periodicity in properties
Hydrogen
S Block elements (alkali and alkaline earth metals)
P Block elements group 13 to group 18 elements
d- and f - block elements
Co-ordination compounds
Environmental chemistry
General principles and processes of isolation of metals

MATHEMATICS:-

Mathematical induction
Permutations and combinations
Mathematical reasoning
Complex numbers and quadratic equations
Matrices and determinants
Sets, relations and functions
Limit, continuity and differentiability
Integral calculus
Statistics and probability
Trigonometry
Co-ordinate geometry
Three-dimensional geometry
Differential equations
Binomial theorem and its simple applications
Sequences and seriesVector algebra

For more details go through

https://engineering.careers360.com/articles/jee-main-syllabus/amp

With the help of syllabus of JEE Main you can plan your studies and focus on topics that will require more time and concepts which can be mastered easily.

Thankyou