First off, you need to study your 12th in Physics, Chemistry and Mathematics. Then you have to appear for JEE Mains. There is no minimum aggregate criteria to appear in JEE Mains. Once you appear in JEE Mains, based on your percentile your rank can be determined. To caculate your rank with the help of your percentile, we should use the formula:(100-your total percentile)*869010/100. Now this is for January session as 869010 Candidates appeared for JEE Mains. Now lets say you are not content with your rank. You can also appear for JEE Mains April session. Based on the State you belong to, you can either appear for JOSAA or State level Counselling and take admission in Aeronautical Engineering in B/B.Tech.