Well, few days remain for JEE(Main). I would have done the following if I were:

Case 1: A student who has studied well in classes 11 and 12 and is having a good grasp of topics

1. All board exams have around 4–5 days gap between them. I would use at least 2 days out of these to solve JEE(Main) material. Rest for boards(do it at your capacity level, boards before JEE, but don't overdo boards preparations.
2. Make a list of your weak topics and start solving the first (easy) exercise of these topics from your coaching class module/book. Try covering all these topics before April.
3. Solve full length JEE(Main) papers and analyze them to see where you lose marks. For my case, mostly it was silly mistakes.
4. Try solving the papers in 2–2.5 hours. I used to score around 310–340 marks in these 2.5 hour tests of JEE(Main) previous papers. I kept on analyzing my mistakes and that lead me to my score.
5. Use the board preparation period for studying NCERT books really well, specially in chemistry. A lot of easy questions will come from chapters like environmental chemistry and you will lose marks(again, it lead me to my score).

Case 2: A student who attended coaching/self studied with a lot of effort but doesn't expect much

1. You are probably a slow learner, but since you have worked hard, you will do well. Trust me on this one.
2. Your weak topics list can include topics you don't know anything about. Cover them first. Just NCERT, notes and exercise 1, no fancy stuff. Then go for slightly less weak topics, and so on. Your focus should be on covering as many topics to the basic level. And boards should be a priority too.
3. First cover topics to a decent extent for few days(solve questions with a timer), and then start solving question papers. Take full 3 hours and try to cover as much as possible.
4. Point 5 in case 1 as it is.

Case 3: No coaching/studies in last two years but want to do something in Main

1. Well, prepapre for your boards well. Learn each and every line of NCERT so that chemistry is covered at least.
2. Join some crash course/one month preparation book

This is all I have to say for Case 3(not much experienced about this).

Case 4: Droppers

You guys already know the stuff. Just keep track your mistakes last year(again, not much experience).

The few days after your second last board exam and before JEE(Main) are the most important. It can change your score by a lot. Do a paper everyday, once your course gets completed. I solved JEE(Main) papers of 2013–16 in last 4 days. Study (at least) Chemistry NCERT books of 11th and 12th. Revise everything once again. Fill your gapholes. Stiffen your upper lip up. Start wing positive. Avoid negative people. Talk to your teachers and parents.

The time which remains can affect your future life a lot. Don't take any pressure due to all that, but do keep it in mind before you think of wasting your time.

You only get one shot, do not miss your chance to blow, this opportunity comes once in life time yo!!!

All the best!!!

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