In order to prepare efficiently for JNU entrance, you will need to study smart. Read the editorial and international relations page of Hindu and IE to get a fair idea of what is happening around the globe. Read Arihant’s guide for JNU entrance for IR. Rafer to some good magazines like Frontline, EPW, etc. 

The exam of JNU Entrance would be computer-based and Multiple Choice Questions would be asked. Make sure to study the following crucial portion of International Relations (IR). 

• Period of Cold War
• Treaties like CTBT, NPT, Kyoto Protocol
• United Nations
• Bretton Woods Institutions (IMF, WB, WTO)
• Environment Topics like Climate Change
• Indian Foreign Policy
• US Foreign Policy

The majority of questions in entrance will be from History, Economics, International Relations, Philosophy, Indian Politics, and Contemporary Issues.

Here are some books that you can refer to. 

• The Globalization of World Politics - Baylis, Smith & Owens.
• India after Gandhi - Ramachandra Guha
• International Relations in the 21st Century - Pushpesh Pant
• Global Politics - Andrew Heywood

Just prepare thoroughly without losing faith in yourself and be honest with your studies and you shall do well in your entrance.