Essence of MSQE(Indian Statistical Institute) Entrance Exam

First things first, your preparation needs to be pattern independent and you must solely focus on covering the length & breadth of the Syllabus. That being said, Mathematics & Economics are the two subjects you need to study.

For Mathematics:
Get hold of any JEE level objective book (Check in Amazon from here) and cover the full syllabus of MSQE entrance examination's Mathematics portion

For Microeconomics:
Intermediate Microeconomics: A Modern Approach by Varian (Check in Amazon from here)
Intermediate Microeconomics, Test Bank by Varian

For Macroeconomics:
Mankiw's book (Check in Amazon from here)
Dornbusch, Fischer,... (Check in Amazon from here)

Reading the above books is essential but practising the previous year question papers is the most important part of MSQE entrance preparation. You can get it from Indian Statistical Institute's website.

Personal Tip : Go through Amit Goyal Sir's Quora & Youtube Pages