hello deepanshu!!

first step is that you see interviews of toppers and their testimonials to get a brief idea about the process but dont blindly follow those.

next see syllabus and previous years papers and go through them properly and observe the trend and type of questions they are asking.

next make  a list of standard books and get ncert textbooks 6-12 of all major subjects in upsc.

go through the ncerts first and read them and simultaneously start reading newspapers.

if you have any mentor who can guide you it would be better.

all the best

thank you