Complete your ncert books before coming to Delhi
After completing the graduation from your respective colleges you should not immediately rush to Delhi for your preparation but stay at home and read ncert.
Accumulate knowledge from your home itself whatever things are needed in upsc preparation.
Complete reading your gs books at least one time so that whenever you come to Delhi you will be aware what to read and what to leave during preparation.
Whenever you will start studying you will be easily able to retain from whatever being taught from the coaching institute.
Basically upsc is not how much you study but how much less books you study but multiple times.
Take coaching from a good institute
Take a good coaching institute from the knowledge you accumulated such as Vajiram and Ravi , Vision IAS, Drishti IAS, Unacademy , Sarathi IAS , Rao Ias, Shri Ram IAS etc.
A good coaching institute gives you proper understanding of and daetails of what to read and what not to read.
Because upsc has a vast syllabus which cannot be completely finished it requires proper scrutinising.
Completion of the optional subject on the same year can reduce your time of preparation as studying optional on the second year can increase your time of preparation.
Optional subject should be revised at least once before prelims.
Write daily answers and revise daily