To clear Civils and become an IAS officer, you have to cross 3 steps i.e. Preliminary Examination, Mains Examination and Personal Interview. First off you need to complete your Graduation because the basic eligibility criteria to apply for Preliminary examinations that you should have a Bachelor's degree. The Prelims exam has 2 papers which test your General Knowledge and Aptitude. You move on to the 2nd round which is Mains only if you clear the Prelims. The subjects that you have studied un your graduation help when you have to take 2 optional subjects during your Mains exam. Because Prelims is all about General awareness and aptitude, say you have cleared it, now you get to choose 2 subjects of your choice in Mains. Now this is where your degree will help you. Candidates get to choose a language of their choice. So if you have done your BA in English, you have a chance in this section to score good. Even if your degree has any of the subjects among Economics/Geography/Geology/Indian History/Philosophy/Psychology/Sociology, you have an upper hand among many other aspirants because with proper preparation and the ability to produce your thoughts on the paper, you can score better.