Engineering Entrance Exam

Few basic tips:
1) If you are appearing for JEE Main then before anything else, have faith in yourself and your hard work. Be positive and let your mind understand that if you can dream it, then you can definitely achieve it with your sincere efforts.
2)Made a timetable for JEE Main Preparation. Devote time to each subject as per your weaknesses and strengths. Coaching experts also believe that having a proper timetable proves to be very helpful for the students.
3)This is the time when you should be working towards strengthening the most important topics of each subject- Physics, Chemistry and Mathematics. Not all topics carry equal weight age of marks. Some topics carry more marks, while others don't. For example, in JEE Main Physics Syllabus of previous year, the theory part (section A) has 80% weight age while the practical component (section B) holds 20% weight age. Devoting much of your time on such topics that carry comparatively more weight age is recommended. You just need to practice such topics more.
4) You must have completed a major part of JEE Main Syllabus which means that you will be able to solve questions that appeared in last years. Solving previous year papers is the most important and required thing to do if you want to excel in JEE Main
5)Avoid distractions: This time is the time to focus on your studies only, as all the other things can wait a little bit. Don't let any distraction come in your way during JEE Main Preparation. You can always get back on social networks and friends, but this precious time should only be dedicated for studies.
I hope this helps you!

It is good that you are pretty serious about cracking these exams
First of all note that your board percentage has no role to play in deciding your JEE rank from this year on wards . So if you can make it a 75% + in your boards that is more than sufficient .
Coming to your preparation
since you are from a state board make sure that you purchase NCERT books .
Read these books simultaneously along with your board books. It is most important to highlight important points from NCERT
Maintain a formula book for each subject note down all the formulae you come across and derivations if necessary keep revising the highlighted points and formulae
Practice from HC Verma for physics Arihant series for mathematics P bahadur numerical chemistry or GRB for physical chemistry JD Lee for inorganic (Balaji publications is also good)any reference for organic is fine
all these things only after NCERT
Apart from these you can practice from Arihant DPPs
and you must solve previous years questions after completion of each chapter
All the best !