Hi
As you are in 12 right now so you should prepare for ur 12 also and there is 1 year left for jee mains so you have time for that .Complete your NCERT before referring to other reference books,it will also help you with your Boards. Once you are done with your 12th,start revising your 11th syllabus. Focus on the chapters that carry more weightage. Go through the previous year papers and get accustomed to the questions asked in exam. You may join a coaching Institute that prepares for JEE Mains. But,ultimately self study is the key to ace the exam. And for exam update I should visit site I am referring.
https://jeemain.nta.nic.in/

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