First know the syllabus for the exam thoroughly. Then start preparing for the exam. Having too many books would lead to confusion during revision. You should only go for books that you've studied in your under graduation. Also study some general awareness about South Asia and the world. Practicing previous year question paper and sample papers would help you to understand the exam pattern, what type of questions exactly come.

https://university.careers360.com/articles/south-asian-university-admissions