Hello Aspirant ,

It is very good to decide your aim this early in your life as it will give your enough time to prepare for UPSC CSE examination ,if you are thinking about starting your preparation  after completing your class 12/from the first semester of your college you should start with basic NCERTs book of class 6-12 and give it proper 1.5 to 2 years as they are the base for your UPSC preparation and then from the 4 semester you should move on to other books like Laksmikant , Spectrum etc you should also start News paper reading .

You should start answer writing practice from the beginning of third year and then solve PYQs from 4th year .

Hope this helps.