Hello Durlav,

For preparation of exam, the most important thing is your confidence after that you should know the whole syllabus and make your plan properly for learning new chapters, solving the numericals and revision. All three things should be the part of your preparation strategy in daily routine.
Your basics in Physics, Chemistry & Mathematics should be very clear upto 12th std. You should read the NCERT books for basics. Then HC Verma for Physics, RD Sharma for Mathematics, OP Tendon for Physical & Inorganic Chemistry, and Organic Chemistry of "Arihant Publication" for detail or extra knowledge. 
You should also try to solve the previous years question papers, this helps too much and you should also give the mock test to rectify yourself and build your confidence level.
For preparation tips, importants topics & the best books, you can go through the link given below
Https://engineering.careers360.com/articles/jee-main-2019
Thanks for query on this platform, you may visit again
All the best for your examination.

For JEE Main follow this Books as Few Months left so please make a preference and don't give much time in finding books because You now don't have much time to try books:

Mathematics: First Master NCERT then Go For Uniques questions of RD Sharma but be very selective and then You can go for ML Khana or Arihant Books:

Chemistry: You must to able to remember every single line of NCERT if You are Not comfortable in it then There is No use to go to other Books, One You are done with it solve all Previous year IIT questions and the You can go for P Bahadur, Solomons, JD Lee.

Physics: No books can compete with Concept of Physics so solve it if You have solved it once then Go for solving it again, also solve some Problems of IE Irodov.

Hello,

The best book to prepare for JEE Mains is NCERT, fisrt go for NCERT books for each subjects.

Apart from NCERT books other books which helps you are:

1. For Physics 

• HC Verma Concept of Physics Part 1.
• HC Verma Concept of Physics Part 2.
• IIT JEE Physics by D.C. Pandey.
• Problems in General Physics by I.E. Irodov.
• Physics for IIT JEE by Resnick, Halliday, Walker.
• Problems in Physics by S.S. Krotov.

2. For Chemistry

• Organic Chemistry by Morrison Boyd.
• Organic Chemistry by O.P. Tandon.
• Inorganic Chemistry by O.P. Tandon.
• Modern approach to chemical calculations by R.C. Mukherjee.
• Numerical Chemistry by P.Bahadur.
• Concise Inorganic Chemistry by J.D. Lee.

3. For Mathematics

• IIT Mathematics by M.L. Khanna.
• Differential Calculus by A Das Gupta.
• Class XI and XII Mathematics by R.D. Sharma.
• Trigonometry, Geometry Books by S.L. Loney.
• Problems in Calculus of One Variable by I.A. Maron.
• Higher Algebra by Hall and Knight.

Hope this will help you. All the best.