If you're planning to apply to SIBM, you should take the SNAP as they don't accept the CAT. It's important to score around 100 marks on the test to have a chance of being called for the interview. Similarly, if you're interested in SPJIMR, you need to score at least a 95%ile in CAT to have a chance of being selected for the interview round. However, students with excellent profiles and extra-curricular activities can get selected with as low as 85%ile.
It's crucial to do your groundwork before attempting any exams, including the CAT. Here are some of the suggested steps:
You can do the above exercise yourself or meet up with a counselor who can help you. However, it's essential to do this exercise because your career is at stake.