Civil Services Exams (popularly known as IAS Exams) are being conducted every year in India to fill prestigious posts like IAS (Indian Administrative Service), IPS (Indian Police Service), IFS (Indian Foreign Service), IRS (Indian Revenue Service) and many other central government services. The Civil Services Exams (IAS Exams) are conducted in three phases.
Preliminary exam (Civil Services Prelims) in June/July
Main exam (Civil Services Mains) in September/October
Personality test (interview) in March/April of the following year

IAS Prelims is an objective-type test that acts as a screening test to Civil Services Mains exam. Conducted annually on a Sunday in June/July by Union Public Service Commission of India, it consists of two compulsory papers of 200 marks each Paper - Paper I (General Studies) and Paper II (General Aptitude) The questions will be of objective type. The marks in prelims will not be counted for final ranking, but just for qualifying for the main exam.
A candidate’s rank in UPSC Civil Service Exam depends only on the mark scored in Main and Interview.
Civil Services (Preliminary) exam is an objective-type test. It consists of two papers. Paper-I (General Studies) is all important as its score is counted for selecting candidates for the Civil Services (Mains) exam. Paper-II (General Aptitude) is of qualifying nature and it is enough to pass (score at least 33%) in it. So, score of Paper-I of all the candidates who qualify in the Paper II (66 or more out of 200) will be used for selecting candidates for the Civil Services (Mains) exam. Scores of the Civil Services (Preliminary) exam will be used only for for selecting candidates for the Civil Services (Mains) exam and will not be counted towards the final merit list

Minimum score in Paper I (General Studies) of candidates in each category in the last few years (the score of the last candidate selected for Mains)

Civil Services Mains Exams are subjective exams (short answer and essay type questions) that are generally conducted in September/October. The score obtained in the seven papers of Mains (four general studies papers, two chosen optional subject papers and one essay paper) will be used to short-list candidates for interview (personality test) The combined score (mains and interview) determines the final ranking for postings. All the seven papers of the Mains carry equal marks (7x250 = 1750 marks) Typically, scores of 800 and above (out of 1750) are sufficient for a general category candidate to qualify for an interview call.

Minimum score (out of 2025) of candidates in each category in the last five years (the score of the last candidate selected for posting)

Every year, UPSC constitutes many interview boards for the Civil Services Interview. Typically, each board consists of six eminent persons with varied specializations and expertise. UPSC member of the board will officiate as the chairman. IAS interview typically revolve around candidate's background and current affairs. It generally lasts for about 40 - 60 minutes. The interview is for a maximum of 275 marks, so it has about 14% weightage (275 out of 2025). The interview board will assess the candidate’s appearance, manners, poise, alertness, emotional balance, rational and unbiased judgment, decision making ability under stress, depth of knowledge, communication skills, analytical skills, leadership skills and integrity. Each interview will generally last about 30 - 50 minutes. Each board is adept at making each candidate comfortable by starting the interview with pleasantries and ice-breaker questions. So the friendly interview boards make sure that the time flies in the interview room and most candidates admit that the interview was pleasant and not at all intimidating. Candidates are allowed to choose their preferred language for the interview from the list given by UPSC and it need not be the same medium that the candidate chose for the Mains
Any score above 200 is very impressive and scores above 250 are extremely rare. Preparation should start soon after the Mains, without waiting for the result of the Mains. Each candidate is advised to keep the photocopy of the application form he/she has filled for the Mains as to prepare for any question about the data that was on the form. Prepare for questions on your home town, home state, your present and past jobs and your hobbies. Brush up your optional subjects for any question. For current events of national and international significance, read good news papers and magazines everyday (see book list for recommendations on newspapers and magazines) Participate in as many mock interviews as possible with a good institute or with your study group.
Interview questions broadly fall into eight categories: 1) Questions about your place of birth/hometown, your home state and your current place 2) Questions about your hobbies 3) Questions about your school/college/University 4) Questions about your subjects/specialization at school/college/university 5) Questions about your optional subjects 6) Questions about your current/past jobs (if you have worked or working currently) 7) Questions current events of national and international importance. 8) Surprise questions or stress questions