Which NCERT’s are important for UPSC Civil Services Examination:

• History: For prelims, just read the New NCERT’s of classes 6th (Ancient history), 7th (Medieval History), 8th (two books on Modern History), 12th (Three books: Theme 1 for Ancient, Theme 2 for Medieval, Theme 3 for Modern). For Mains, you need World history books (9th and 10th classes). In 11th class, read only few chapters required for the syllabus. Similarly, Modern history books are not very good (8th and 12th theme 3). So, read old NCERT modern History by Bipin Chandra. “An Introduction to Indian Art” is important for “Art and culture” and it is a good replacement to Nitin Singhania for those who do not have time. 
• Geography: Focus more on 11th (two books) and 12th (two books) as all the concepts of Physical Geography and Human Geography of India and World are covered in this. If you have time, quickly go through 6th to 10th books but need not remember the facts in them. 
• Economy: 9th, 10th and 12th (Read only Macro Economics but not Micro Economics) books have concepts that are required to understand current affairs and get confidence in Economy. But 11th class book is important to write Essays and Mains answers on Indian Economy. But focus more on current affairs than NCERTs when it comes to Economy.
• Polity or Civics: Most important books are 11th class (Constitution of India at work) as it is similar to Lakshmikanth and some rankers who read this 11th NCERT never touched Lakshmikanth book. 12th class books are important for other subjects like “Contemporary world politics” is required to understand International Relations and “Politics of India since Independence” is important for Post-Independent history in GS-1. The NCERTs of 6th to 10th are not very important but giving them a quick glance can help in building basic idea of Indian polity.
• Society of India: The 11th and 12th NCERTs are important to write GS-1 Mains answers
• Disaster Management books of 8th to 10th NCERTs is important for GS-3 Mains
• Environment: Last 4 chapters of NCERT 12th class Biology 

How to read NCERT’s for IAS exam:

• As per the above description, divide the books into “Important” and “Not so important” categories. 
• Spend more time on “Important” books by underlining, making notes, revising them as questions come directly from them
• “Not so important” books or books which can be replaced by standard books need to be given a quick glance. Do not waste time in by-hearting every word in that book. 
• Several questions of UPSC Prelims and Mains directly come from NCERTs.