In order to score good marks in JEE make sure your concepts are clear. To build strong basics you can refer NCERT books and you should also solve NCERT exemplar.
Make sure you are aware of the full syllabus, exam pattern and Important topics. Focus on the important topics. You can make your important time-table according to your comfort. So, that you complete your syllabus on time and you get proper time for revision. You should focus on quality rather then quantity.
You can refer previous year papers to understand the exam pattern and level of questions.
To crack JEE exam you need to practice a lot. You can solve as many as MCQs for your practice. You can also solve timing test to work on your time management and to increase your speed. You should also solve complete mock test series to analyze your preparation level at regular interval of time and to know your strength and weakness. So, you can work accordingly.
Revision plays a important role in your preparation. Don't avoid it. You should give proper time to revise your complete syllabus specially is Chemistry. You can take help of your notes if you have prepare them. Revise all the formulas as well.
If you want to score 260+ marks in JEE it is very important to solve 70-80% of your exam.
If we check the last year trend then chemistry is the easiest section. If you want you can solve it first. So, that you can give proper time to Maths and physics.
All the Best for your Preparation!!