I’ll just confine my answer tailored to the needs of Preliminary Examination and the GS Papers in the Mains. As for optionals, consult people who are already preparing in those topics.
Let’s start with the bare essentials.
- NCERT Textbooks: You should read the basics from NCERT Textbooks. That raises the question, whether you should read all the NCERT Books cover to cover. Reading all of them can give you a thorough grounding. However, it is largely not needed. The following is my recommendation.
- Class VI: Social Studies: Earth: Our Habitat: Chapter 8
- Class VI: Science : Chapter 7, 9, 16
- Class VII: Social Science: All chapters
- Class VII: Science: All chapters
- Class VII: History: Al Chapters
- Class VIII: Resources and Development: All Chapters
- Class VIII: Science: Chapters 1, 2, 7, 18
- Class VIII: History: All Chapters
- Class IX: Social Science: Contemporary India: All Chapters
- Class IX: Science: Chapter 14, 15
- Class X: Social Science: Contemporary India: All Chapters
- Class X: Science: Chapter 14, 15, 16
- Class X: India and the contemporary World: All Chapters
- Class XI: Both books of Geography complete
- Class XI: Chemistry: Part 2: Unit 14
- Class XI: Indian Economic Development: All Chapters
- Class XI: Indian Fine Art: All Chapters
- Class XII: Macro economics
- Class XI: Indian constitution at work: All Chapters
- Class XII: Biology: Chapters 12, 13, 14, 15 and 16
- Class XII: Themes in Indian history: All Chapters
- Indian Freedom Movement: By Bipan Chandra. Study this book thoroughly and be done with Indian history. No need to mug up from any other books.
- Norman Lowe/ NCERT World History: Going by the pattern of recent years, there is no need to mug up Norman Lowe. NCERT World History will cover you for GS I
- Indian Polity, Laxmikanth: Be thorough and through with this book. Regular revision is recommended.
- Opinion page: The Hindu, Business Standard, Live Mint. These three papers will have you covered. I don’t think you need to read the entire paper to be well informed. For that resort to either twitter or an app like inshorts. Read newspaper to develop opinions.
- Selected chapters from India after Gandhi and India since independence: There is no need to read these books cover to cover. Refer to the syllabus and then read only those that are needed. If you are really interested, go ahead, finish them.
- Economic Survey: In addition to the NCERT Textbooks, and the newpaper reading, this is the only thing you need to read. Don’t waste your time wrestling with Ramesh Singh. In addition to having a lot of unwanted information, his English is really bad. The book is a drag to read.
These are the books that I can remember as of now. If I have missed any topic from the syllabus, do let me know in the comment and I’ll keep updating the list for those topics too.