Dear Singh

I have also been in the same phase as you are in a few years back and so i understand your concerns. To prepare for competitive exams i recommend you to follow a strict time table for all the core subjects that is physics , chemistry and maths. I would recommend you to focus more in maths because it increases your chances to get in your desired university.

Practice previous year sample questions as much as you can. Regularly solve the question papers of namely institutes like FIITJEE , Akash and Resonance , by asking your friends. Feel free to ask questions with your friends who are studying in coaching. Also try to clear your doubts from your  school teachers as much as possible. Also join online communities and whatsapp groups related to the subject.

Occasionally take breaks to relax your mind and get back to your schedule as soon as you feel good enough. I recommend you to read your language subject books like english at the time you take to relax.

Regularly indulge yourself in physical sports or activity to calm your mind and strengthen your spirit. Now just try all these as best as you can and i believe you will get good results at the end.

I hope i was able  to answer your questions , feel free to ask more  

Yes there are many JEE aspirants who prepare for JEE at home and then get good marks. You can take help from online teaching videos which are very helpfull to solve your doubts. i will suggest you to enroll any online jee test series which will help you to know how much you have learnt. Read line by line of ncert for basic concepts and then practice maximum question. just take any of one refrence book for all three subjects like HC verma or Dc pandey for physics, and solve all the questions of it.