Hello!

First, you have to start with NCERT books from 5th std to 12 the std. This you should do thoroughly for at least 1 year to clear your basic concepts.After that you may start with some reference books like Indian polity,India after independence. Also start reading Hindu newspaper daily. Learn to analyze each thing,incidence like their background, reasons,effects,advantages, disadvantages and their correlation with others if there. The most important "START WRITING". With the time u will learn the most important skill for UPSC I.e. to write concise and quality answers. Start with these and will aid you further guidance as you proceed further.

Thankyou!

Hope it helps!