Hii Yash
To achieve good marks you have to study according to a particular schedule so here are some tips which will help you to score good marks
1) divide your day into 4 half's and each half should be of 3 hours atleast,first half should be for physics,2nd for chemistry,3rd for biology and last half for solving MCQ's
2) your main focus should remain on NCERT textbooks as most of the questions are asked from it so make sure you go through your NCERT textbooks thoroughly
3) opt any one reference book for each subject so that you can solve MCQ'S like for physics you can opt universal publication,dc pandey,Allen module,for chemistry vyou can opt Dinesh objective,ABC publication,MTG,for biology you can opt trueman of biology,Allen module,MTG.
4) solve previous year question papers as most of the questions are repeated as it is
5) make it a habit of solving mock test,it will increase your speed of solving questions.
I hope this information helps you.
Thank you