Candidates (general and OBC) need to have secured a minimum 75% marks in class XII or equivalent exam or be in the top 20 percentile in their class XII exam conducted by the respective board. For SC/ ST candidates, the eligibility criteria are to secure 65% marks in class XII or equivalent exam. So you'll have to score 75% in your class 12 boards and you'll have to do exceptionally well in JEE advanced to get into IITs.