What should I do if I have to leave Aakash in December because of some problems and after this how should I prepare for IIT-JEE?

You can also prepare for JEE without joining any coaching institute there are many students who have done that. So, don't worry be motivated to crack this exam. First, complete NCERT book to clear all your concepts and to build strong fundamentals then you can also refer other books according to your choice. Revise thoroughly You should revise the syllabus as many times as you can. Doing so will help you in the following ways: It will increase your test-taking speed. It will help you overcome panic. It will give you a clear picture about the topics you're weak in. Mock test Paper Go through mock test papers to analyze your performance and to know your strength and weakness. You can also refer previous year papers and MCQs for your practice