This question has been asked many times by many people as they wonder if I am also a person who recommends the books to the needy. In fact, I might become one someday but right now, I am not that. Still, I will try to let the readers know this with whatever information I could gather from various sources and various blogs. I will also share some of the links which will really help you with this concern.
You need to be wise and this is the first self-book you need to study before preparing for UPSC which is one of the toughest exams in the world. Once you understand the importance of this exam and the amount of energy it would require from you, you will make decisions wisely and carefully as well. You need to start with changing your habits:
reading newspaper daily
reading magazines that cover government, current events and important opinions nationally and internationally
reading good literature to pass the time between juggling
reading the best books recommended by the experts
reading the basic books which are essential to understanding the fundamentals of the subjects
Once you cross the fundamental stage, you need to take on the important subjects. You have to choose one subject for the purpose and then you can move ahead with other ones like GS, Ethics, Public Administration and many others which form a part of it. For each of the subject opted for mains, there are special books which cover the entire syllabus effectively and are very useful in the terms of IAS examination. For example, there is a certain set which contains the best books to study geography for UPSC mains and there are certain books which will cover English as a mains subject in the IAS. So, you need to identify those sets of wonderful books and start studying according to that.
Once you start studying a particular set of books, you will be pushing for a new level of understanding and that will enable you to find another set of appropriate or advanced books which will make your studies even better and comprehensive as well as wider. Always try to study at least two books for a particular need as this becomes very important in the exams like IAS to have plenty of ideas and plenty of views on a concept. Reading many books will ensure you have that depth in your understanding and rich in your thoughts.
All the best with your IAS preparations guys! Keep rocking and keep chasing your dreams… only the dreamers can make it.