To get admission in IIM Ahmedabad, you need to appear for CAT, first. International students need to appear for the GMAT. Students who score above the required cutoff and composite score, are shortlisted for the WAT-PI round. The final selection will be based on various factors such as your past academics, work experience, CAT score, performance in WAT-PI, etc. IIM Ahmedabad also looks for leadership qualities in students.
Clear your basics in English and Quants. Study newspapers and stay updated with the happenings around you. Solve puzzles. These are some of the things that you can do while preparing for IIM Ahmedabad.
With poor academic records, you will never get a call from IIM Ahmedabad. Yes, if you belong to the reserved category then there is a little chance, otherwise, your chances are none.
You can go through the latest selection criteria of IIM Ahmedabad and by assuming your percentile to be 99.xx, you can calculate your weighted average score. Also, do not forget to calculate the same with the good academic records of someone. By doing this you will find out where you stand and what are your chances of making it to IIM Ahmedabad.
Here is a true story as an example:
My brother studied at one of the top IITs after securing an AIR among the top 10 in IIT-JEE. But, after joining the IIT, because of drug addiction he could not complete his degree on time. He completed his degree with poor academics and because of this even with a good CAT score he did not make it to IIM Ahmedabad. But, he made it to IIM Calcutta.
The point here is, you have chances of making it to the top B-schools but, if you aim specifically for IIM Ahmedabad or IIM Bangalore, you are not thinking effectively.