The best prep books for UPSC exams are as follows:

1. Ancient History: ‘Ancient India’ by RS Sharma (Old NCERT)

2. Medieval History: History of Medieval India by Satish Chandra (Old NCERT)

3. Modern History: ‘A Brief History of Modern India’ by Spectrum as well as ‘Concise History of Modern India’ by Sujata Menon

4. Indian Culture: ‘Facets of Indian Culture’ by Spectrum

5. Indian Geography: NCERT books, Oxford Atlas for maps

6. Political Science- Indian Polity by Laxmikanth, An Introduction to the Constitution of India by D. D. Basu, The Constitution of India by P. M. Bakshi, Old NCERT

7. Economics- Class 11 and 12 ncert, Indian Economy by Ramesh Singh, Indian Economy by Mishra and Puri, Current Economic Survey

8. Science and Technology - newspapers and official websites like ISRO etc

9. Environment - Newspapers, online materials

10 Current affairs - Newspapers, GK books