Firstly I would suggest you to go through well with NCERT books as it will help you to make strong the basic Fundamentals. Here are some preparation tips you can follow:

Work on a Time Table: After carefully checking the syllabus of JEE Main work towards creating a perfect timetable which will fit your schedule while leaving enough time to prepare for the examination within the days left. Make sure to add short and sweet breaks in between for some relaxation.

Make your Basic Concepts Strong: While it is essential to study the topics mentioned in the official syllabus, it is also advised to study the basic concepts well first. By knowing the basic concepts of the units involved in the examination, you will be able to understand each topics well and in depth. This will result in a greater understanding of the topics and will make it simpler for you to study complicated concepts present in the syllabus.

Improve your Weak Points: Stressed over some topics or formulas which you just cannot seem to understand? Give more time and focus on these topics to improve it. Keep small notes and constantly revise those concepts which has been hard to understand. By constantly studying the topics you find difficult.

Write Notes and Prepare Flash Cards: Like discussed in the previous strategy, keeping notes greatly helps during the preparation process. Notes written in small diaries are highly accessible and you will be able to study from them anywhere anytime. By writing down those complicated theories and formula and revising them, you will be able to remember and understand them more efficiently. Similarly, create flash cards to help you with quick studies and revision.

Attempt Mock Test and Solve Sample Papers: Mock tests will give you an almost real experience of how the examination will be. By solving mock tests, you will be able to work on time management while at the same time understanding the question paper pattern.

Revision: While studying it is important to revise those topics which has already been studied. It is advised that each day, a certain amount of time should be divided for revision purposes. Revision is very important as the syllabus is quite vast and all topics have similar importance level which has to be remembered and known by you.

You can check the important topics to prepare the exam with the given below link.

https://engineering.careers360.com/articles/jee-main-important-topics-books

Good Luck!

It is not very difficult task to score more than 140 marks in JEE main you can predict many questions which are important for JEE MAIN and therefore you need to look at those kind of problems and make sure not to miss this kind of problems at  every possible questions on that particular topics. Specifically you can expect a question on ,circles quadratic equation, sequence and series probability electrochemistry, name reactions, inorganic reactions, in organic properties, de Broglie wavelength, young double slit experiment capacitor.