In jee mains basic bt twisted questions are asked .For that you should know the basic concept of each chapter .Try to solve as many questions as you can that will be very much helpful.modern physics inorganic chemistry name reaction in organic chemistry  calculus  coordinate geometry thermodynamics electrostatics  are scoring parts try to focus more on it

JEE main syllabus comprises of three subjects, Physics, Chemistry, and Mathematics.

Chemistry, in General, considered to be scoring, since questions are multiple choice so while studying you should not have confusion regarding any Topic.

In Chemistry You can study from NCERT, look at the previous years' papers and you will get the idea of the question being asked. Look at the question in Previous years papers and try to find whether you are able to solve it or not from your 12th class studies. This is what all about patterns and level of Questions asked in the Exam.

For Physics take help of HC Verma, It is Concepts of Physics Part1 and Part2. If you are able to solve its questions then JEE Main is not a big deal for You.

For Mathematics take Help of NCERT and RD Sharma. Questions will be tougher than what you used to solve while in class 12thg so practice well to be able to solve JEE Level questions.