Mug up  the official syllabus first. World History does not come in Prelims, It only comes in Mains. As you can see that here we have divided whole syllabus in the different four part. (Remember we are concern about World History in this Article).

• Modern Indian History
• Medieval Indian History
• Ancient Indian History (Culture, Art, Architecture, Society and Literature)
• World History (in Mains Exam only)

What type of questions asked?

• Related to implications of key events of world history at global level - like world wars, financial crisis of 1929 etc.
• Evolution of key political ideologies and their impact on global politics - socialism, communism, democracy etc, differences between them, their evolution.
• Related to key events which changed geo-political environment of world - unification of Germany, unification of Italy (role of key individuals in these events).

To decode all these topics see last three years History optional papers related to World History which comes in Paper - 2 (Part-2).

Sources from where you can read World History

There is no single book which has all the topics mentioned and covered properly. So you may have to see the multiple sources. One important book is "Mastering Modern History (3rd Edition | 5th Edition" by Norman Lowe which is a very good book. Its notes format is in very scientific structured manner. Search other specific topics from internet which are not covered in books. IGNOU study material is also a good companion and easily available.

What to read for World History

Here is the list of certain topics which we have compiled in the exam point of view. Make sure that atleast you cover these topics in entirety.

Give importance to such topics:

• American Revolution, constitution, Impact on India
• French Revolution - nature, implications and how it unfolded, reasons including key philosophers behind the revolutionary thoughts (Voltaire, Rousseau etc), impact on India.
• Napoleon Era world politics - particularly European politics.
• How England avoided revolution, development of liberalism in England, evolution of democracy.
• Development of "Nation-states" in Europe, reasons behind it.
• Labor movements, capitalism, socialism and communism, Marx, Indian connection.
• Unification of Germany and Italy, role of key individuals like Bismarck in them
• Russian revolution - reasons, background, and implications
• First World War - India connection, effect on national movement
• Growth of Fascism and Nazism, Global Financial crisis, effect on India
• Second World War - India connection, effect on national movement.
• Colonization. decolonization process (how it unfolded in different phases)
• UN movement, its work, success, failure, efforts before that.
• Cold War politics, NAM movement, EU movement.

Things to do while answering the world history questions

• Try to cover as many aspects of key events while writing an answer. Such as if question is about implication of Russian revolution then you should cover.
  • Global implication at political economic level.
  • Impact on Russia itself
  • Ideological level implications
  • Impact on decolonization process
     
• Think globally but also try to add points connecting with India.
• If many points are there then write point-wise with sub-headings.
• If you can draw maps or any visual representation then it can fetch more marks (obviously you have to manage time).