You must follow these simple steps:-

1. Check out the syllabus and structure your preparation, made a plan on how you're going to cover the syllabus.

The best thing to help you in this is coaching material from some good institute. They have their material prepared according to the need of the Exam.

2. When the plan is ready,make a schedule. Remember timetable matters a lot for this one year. Be ready to give at least 6 hours per day for the preparation.

3. Solve the questions from question banks and previous year JEE papers.

4. Repeat these steps. Follow --> Learn --> practice.

5. Also keep on revising the stuff every third week. It is also a very crucial step in your preparation.

Thank you.

Links:-

https://engineering.careers360.com/articles/how-prepare-for-jee-main

https://engineering.careers360.com/exams/jee-main

https://engineering.careers360.com/exams/jee-advanced

https://engineering.careers360.com/articles/jee-main-syllabus

Comment if you have any doubts.