After 12th, you need to mandatorily complete your Graduation in stream of Interest, be it B.E./B.Tech, B.Sc., B.A. , LLB, B.Com before you appear for UPSC Civil Services Examination. In the final year or after graduation you are expected to formally begin you UPSC Preparation in full stead. Many prepare by self study while many take up proper coaching plans and test series for a proper and strategic preparation.

Overall UPSC CSE, as far as I know is 50% hardwork and 50% strategy. You need a proper test taking strategy, strategic selection of study material and preparatiom resources as well as strategic routine for regular preparation.

For more information about UPSC CSE preparation do follow the link below

https://competition.careers360.com/articles/how-prepare-for-upsc-ias