Dinesh, CAT is the entrance examination for admission to all the 20 IIMs and more than 1000 participating Institutions which include India's top B-Schools. So the competition is tight and you need to prepare as hard as possible. No time is early for preparing for an exam like CAT. IIMs do not have a specific syllabus for CAT. An assumption is drawn based on previous question papers. So, it inviolves Mathematical formulae and analytical thinking. For being good at these, you need to start preparing as early as possible. You are eligible for appearing for CAT once you are in your final year. So, if you start from this year as well, you can get into a decent top B-School.