First thing first, read the NCERT books and start with clearing your basics. For biology, physics, and inorganic chemistry NCERT books will suffice. If possible, get your hands on a set of modules prepared by a decent coaching institute. They do help.

Make sure you go through these books multiple times and prepare notes for the last-minute revision. You must cover the entire syllabus at least twice (or thrice) with the examination.

Take regular mocks and practice chapter-wise MCQs, as this will help you analyze your strong and weak points, in turn, your preparation.