The admission to IIM is depend upon various factors the first step is to have a good CAT score and percentage in class 10th 12th and graduation so different IIM have their different criterias so if a student qualify  criteria then they are invited for the further procedures which involves some IIM have their own analytical written test and other personal interviews so all the three processes have their own weightage in different IIM and there is a different procedure for admission to different IIM so first step is to have a valid CAT scoreand that too in the required criteria.