If you are interested for MBA programmes then after 12th you can go any of the graduation field like B.tech, BBA,  B.com etc. as per your interest.

If your subjects are PCM then you can go for B.tech graduation programme + MBA  after 12th as it will help you to gain a technical & practical knowledge along with Management skills. 

If you go one of these B.Com or BBA programmes then MBA is some easy for you because main and important portion of MBA you will read in these Graduation Degrees. 

To get admission in top colleges for MBA,  You need to appear the Entrance examination like CAT, MAT, CMAT etc. after graduation or during the final year of Graduation. The minimum score in graduation should be 50% to apply for CAT as a general category But there is no any such criteria for other examination like XAT, MAT etc.

After graduation if you have work experience to apply for MBA then it will also give you the waitage to get admission in top colleges like IIM and ISB etc.

Good Luck!