Try to to as good as possible atleat cross 75 % ..
For IIT JEE .. the first very important thing is clear and enhance your concepts .. jus keep this thing in mind that building concepts and practicing a lot is damn important for IIT preparation.. Always start from BASICS because "without base, there will be no altitude… Never prefer solutions of questions before doing SELF-ATTEMPT at least five times till you get the right answer because "without fall you can not stand at once".
Study without loosing the concentration coz studying 2 hours with very good concentration is equals to studying 5-12 hours without any concentration. . and have a confidence in yourself.
All the Best.