There can be find n number of book lists and sources on the internet but the most important sentence before you start collecting your sources to gear up your preparation….
“What not to read is rather more important than… what to read!!!”
So be confined about the sources you read… Your knowledge should be qualitatively stronger than quantitively.
PUT A STRONG FOUNDATION…
NCERT, s can be taken as the building blocks of your foundation, because they not only help you to gather knowledge but also give you a good reading and sitting habit which is a must for Civil services Examination. Start with 6th to 12th standard books of History, Geography, Polity (Civics), Economy (Specially class 11th & 12th) etc.….
There are some standard books which you can follow to cover the UPSC Prelims syllabus…
Ancient Indian History- R.S Sharma.
Medieval Indian History – Satish Chandra.
Modern Indian History – Spectrum, Old NCERT, Bipan Chandra.
Art & Culture- CCRT & NCERT, Nitin Singhania.
Class 11th & 12th Book of Tamil Nadu Publication.
Or else check Compilation of EDEN IAS Ancient, Medieval, Modern, Post Independent India, Art & Culture, World History.
NCERT Class 11th & 12th, G.C Leong, Orient Blackswan Atlas or EDEN IAS Compilation of all standard sources.
NCERT Class 6th -12th, M. Lakshmikant, Or else EDEN IAS Compilation of all standard sources.