Hi there.

For becoming an IAS officer one needs to write the UPSC examinations which require all-around knowledge of all subjects. Hence, there are various interesting subjects to choose from. 

You should choose a field of graduation that you are passionate about, in which your interest lies, and something that helps you in your preparation of UPSC exams as well, you can opt for a BA in History, Geography or Political Science. Even a BSc/BA in economics would be great too. 

Start your preparation from the very 1st year of graduation. Start with NCERT books of Class VI-XII of History, Geography, Economics, and Science. 

Develop a habit of reading The Hindu daily and be updated with current affairs. Read the Yojana Magazine regularly. 

For a proper book list and study schedule head to Unacademy's website (Roman Saini's lessons) and Mrunal's blog. 

Hope this helps.

You can choose any ug course in which you interested every course will provide you equal opportunities so it depends on you in which you are interested