Hey!
If you have scored good enough percentage in 10+2 board examinations(i.e., above 90%), then you can apply in University of Delhi for undergraduate degree. The studies are far better here than other central universities across the country.

Many coaching institutes offering UPSC Prelims+Mains extensive study programmes (coachings) are located near colleges of DU, especially in North and South Campuses. 

Go through the list of optional subjects in UPSC Mains. Choose the subject which you like and then opt for bachelors honours in that subject, or a programme degree with your subject of study included in the curriculum.

Best wishes!