Especially if you are from a political science background, make sure you have deep knowledge about the topics that you have covered during your graduation. The questions that appear in the entrance examination usually focus on topics like Classical Political Philosophy, Indian Political Thought, Indian Politics, and International Relations

Suggested Readings

1. Classical Political Philosophy - Sushila Ramaswamy or C.L.Wayper
2. Indian Political Thought   - Thomas Pantham or B.R. Mehta
3. Indian Politics - Oxford Companion to Indian Politics, and read the book by Bidyut Chakravarty and Rajendra Pandey on Indian government and politics.
4. For theoretical understanding, - Baylis and Smith.

 Never skip current affairs, which is an important part of the question paper, and try to improve your writing skills for better results.