We tend to push studying until the last second, even for board exams. Since board exams are already creating a lot of panic and you guys are already stressed, here are a few of my tips to ace board exams that can make your lives a little less stressful.
There are three main subjects that need to be focused on:
For Physics, Chemistry, and Maths. For all these subjects, a full run-through of the NCERT is crucial. You are bound to find certain topics that many other books might have not covered. You also need to go through previous year papers in order to determine FAQs and have them written down. This comes in handy at the time of revision. Also, practice the exercise questions at the back of the textbooks to get hands-on, on numerical. 
For Maths- There is no other way and the only thing you need is practice every day to perform well. Make it a point to play a sport daily, during the days of your preparation. This will keep your mind and body active. Meditation and yoga can also help to gather more focus on preparation.

Make sure you leave the books at a maximum of 11 pm the night before the exam and get a full night sleep, a minimum of 8hours is a must. It is good to talk to your parents, friends, mentors; someone you are comfortable and let them know if you’re stressed or nervous. Help is at hand, only if you reach out to them. Join a study group and look at studying aids for the exams. Make sure you get good advice and mentorship from teachers and from people who passed. Work hard and be confident, you got this! Good luck.