Hello student, 

I'd just suggest you to mug up the NCERT books first.

Take pre-boards seriously. 

As most of the time, your board practicals marks are awarded on the basis of pre-boards. Even externals also ask you about your pre-boards performance.

Not only this, pre boards will tell you your current status about how much you're prepared for boards.

So,make sure you get 30/30 in three of the practicals.

Now, for theory exams
First and foremost thing is to mug up NCERT books. Get through it. Boards paper constitutes direct questions from NCERT.

For chemistry, NCERT book is more than enough. I'd not suggest any reference or previous year books.

For maths, the question paper will surely constitute of 50% direct NCERT questions.But in maths, you need to do previous year papers. For this, get U-like book and solve each and every paper. This will help in managing time to complete paper in 3 hours.Time management is must. 

For physics, it is going to be a little tough as compared to other subjects. But if you're thorough with concepts,90+ is easy to score 
Practice each derivation. Get through the numericals. For physics too, purchase U-like and simply solve all the solved papers.

For english, Time management is equally important. You don't really need to use fancy words in writing section. Be direct and underline important points. Do the character sketch for novel section.

Hope this helps.... All the best