First of all you have to clear prelim i.e. CSAT consisting of two papers
1)General Studies-200 marks
2)General Aptitude-200 marks
Then after qualifying it,You have to give mains (2000 marks)
1)GS-2papers-300 each
2)Optionals-2-300 each
3)essay-200
4)English-300
5)One of the languages to be selected from 8 th schedule-300
Then,after qualifying mains exams,you will go for interview round-300 marks
Total exam=2700 marks.Many good coachings are there in Delhi..Someone of them are Rau's,Vajiram & Ravi,etc..
This is what I know.For a more detailed knowledge,please visit www.civilserviceindia.com.