Dear Moni,

First and foremost best reference for UPSC Civil service exam is NCERT Books.

NCERT Books helps you to write answers in mains examination and improves your language skill..

For the basics you need to study the 6-8 standard books of History, Geography, Polity..

For economics you have to study the books from 9th standard..

For the reference purpose you refer the some of the reference books..

Thank you..

Dear Moni,

Here are the best books for civil service exam -

• Indian year book (current affairs).
• Indian polity for civil service examination by M.Laxmikanth.
• Indian art and culture by Nitin Singhania.
• Oxford school Atlas by Oxford publishers.
• Indian economy by Ramesh Singh.
• Economic survey by Ministry of Finance.
• A brief history of modern India by Rajiv Ahir.

Regards