Dear student.

Greetings.

For a well structured JEE main preparation, you should start with the NCERT textbooks. You must read and solve the NCERT textbooks in such a way that you are able to solve any question from it easily. Then, you should opt for reference books which will provide you deeper explanation on the topics. Also, you should solve past 10-15 year question paper in order to clear JEE main examination. Do all these and you will surely clear JEE main examination.

Thank you. All the best.

You can start Your Preparation along with Your class 12th Preparation since JEE Main has the same syllabus as your class 11th and 12th, but the level is slightly higher. 

While studying for class 12th understand the concepts Properly take help of previous years questions of JEE Main. There is a subjectwise different strategy that you need to follow. For Chemistry, you should read NCERT. For Physics take help of Concept of Physics by HC Verma. Mathematics can be scoring if you practice enough. You should solve all the miscellaneous exercise questions followed by Questions from RD Sharma.