To get admission in tier-1 colleges of MBA ,firstly you have to recieve a call from the colleges. And to recieve a call you must have a good score in CAT,XAT entrance exams. SO, firstly i recommend to work hard on entrance exams and secondly if you have a work ex or good portfolio then if you have some sort of low score in 10 and 12th. then they consider it but the first and foremost critria is good score in entrance exams