Civil Servant (IAS/PCS)

Hi Kartikey,
After class 12th, your approach should be to focus on the static areas such as history, geography, polity, environment and general Science. You need to clear your basics regarding these subjects as they form the 60-70% basis of prelims examination. The books you can initially refer are NCERTs of class 6th-10th for Science and environment, and for other mentioned subjects from class 6th-12th.
A lot will also depend on, which course you will opt for your graduation, as a lot of areas would be covered in your higher studies. There are a lot of options available such as B.A, B.Sc, engineering, medical, etc. But the fact of the matter is, where your interest lies as all these subjects have their own importance in the examination. Like, subjects under B.A. courses such as history, geography, political science are helpful in prelims and mains stage. On the other hand, engineering gives you the advantage of analyzing and answering in a lucid and crisp manner.
Moreover, newspaper reading is a must habit which cannot be dispensed with. With new digital mediums available, it is easy to access news and current affairs. In the coming years of your preparation, also try to inculcate how to utilize time and form an opinion on various socio-economic issues happening around us.
For the mains and interview stage, there is a long way and UPSC might make changes in the examination pattern, so that part can be dealt later.
All the best.