Board exams are near. Pressure must have increased. You must be thinking how to handle so much pressure ? Boards -> JEE Main -> JEE advanced !!
Life must be going too difficult. I know how it feels. I have been through the same last year.
Let me help you to make it a bit easy.
Most probably, your first exam will be English (you must have got your date sheet by now). Prepare whole heartedly for it. Dedicate 3-4 full days for it. Keep your JEE preparation aside and start preparing English. There are many guide books available in the market and they are really really helpful especially if you are a dummy school student (Like me :P ). It's very important to get at least above 80 in English otherwise your percentage will go down significantly (Remember you have to be in the top 20 percentile of your board). Read the text book prescribed for your board thoroughly and follow a guide book. Ask for help from your friends who are not preparing for JEE. Request them to teach you English lessons.
Attempt the paper with planning and everything should be fine.
Around 50% load should be gone off from your head after English paper is over.
Next usually you will have Mathematics then Physics then Chemistry.
Here is where the trick comes.
You have a great chance to prepare NCERT thoroughly. Study NCERT in great detail. Solve the examples given in maths book. They might seem trivial but remember that if you don't have a practice of "writing" a solution, then you will be facing problem in your Board exams. So better sit with a pen and paper and write down the solutions to even the easy questions. There are certain topics that are not present in JEE advanced syllabus but they are in Board syllabus. Make sure you cover them. That will not only help you in Board exams, but also in JEE Main.
Do the same with Physics and Chemistry (especially). Prepare NCERT thoroughly and you will be done with class 12th syllabus of JEE Main and JEE advanced too (partly). In this way, you aren't wasting your precious JEE time. Instead, you are utilizing it smartly.
Make sure to cover all the proofs and derivations in Physics. They are important.
Make sure you have seen papers of last 3 years and solved them properly.
Make sure you have memorized all the tables and diagrams mentioned in NCERT for both Physics and Chemistry.
Lastly comes the optional subject (Computer/Physical education/Hindi/any other).
For Physical education, you don't really need to burn the midnight oil. Just learn the headings and write the final answer in your own words. You will surely get 90+ but make sure to dedicate around 2 days to the optional subject.
Getting a 90% in Boards is not only easy, but also it is required especially if you are in ICSE or CBSE Board.
For CBSE, the GodBook is NCERT. Don't search for unnecessary guides and all. Guides are required for English and optional subject. For Physics, Chemistry and Maths, you don't really need a guide. You JEE preparation experience is sufficient.
Whatever I have written in this post applies by and large to all the boards. Syllabus may vary slightly. Make sure to follow the syllabus strictly. You should not end up wasting time on something that is not really required.
All the best.
Work hard and make everyone proud of you.
Comments and suggestions are welcome.
A post on JEE Main will be coming soon