IIM Ahmedabad - Indian Institute of Management

First of all it would be dependent upon your profile, score of graduation, 12th and 10th but in CAT examination you have to score very high about 98+ percentile.

To get into IIM, you need to write CAT exam. After CAT, if you get the eligible percentile to get into IIM then you have to face a personal interview in any of the prescribed IIM from your choice based on the marks. Sometimes, even you get 100 percentile in CAT, you may not get an IIM, all you need to do is maintain sounding academic background with good communication skills. This would certainly help in shortlisting you.

Your graduation score is a bit less, I would thus recommend you to try for a very high percentile - in the high 90's to stand a chance.

You should apply and then see for yourself, the criteria is highly subjective based on every year's participants.

To be very honest with you, it looks very difficult to get admission in a top B-school. But still you may apply to tier-2 or tier-3 MBA colleges in India.

Only the latest year's CAT score is considered for admissions, you need to appear for CAT in the very same year in order to apply for admissions.

A regular PGDM will be suitable for your profile.

Start by solving Maths problems given in previous CAT exams (You can find books containing the same).
The rest can be covered easily while preparing from an institute.

Yes, you need to score well in CAT. If you have an Engineering background, it might be really tough but nevertheless do not skip CAT training.