Languages

You should use your study till now to your advantage. You can increase your score in main due to English language. Similarly, by choosing main subjects in allignment with preparation of pre should be another startegy. History, Geography, Polity, GS, Economics has maximum share in pre paper. So you can choose one from among these. I suggest you to do subject wise analysis of CSE pre. & choose a subject which for main which is of interest & in allignment with pre. There are some things which can be regarded as pillar of IAS examination. These are continuity, quality study material & focus on smart study rather than hard. It will take time. May be you plan to do it along with a job for 2-3 years.