You haven't mentioned the specialisation you would like to pursue in your PG. You can check the course list at the official website: https://www.imperial.ac.uk/study/pg/courses/ . You need to decide on that first. And you need to take up an English Proficiency test like an IELTS/TOEFL. The requirements depend on the course that you pick for your Masters. And most applications begin from Mid November. You need to have a Personal Statement, References kept ready. You also might have to attend an Interview via Skype. But the interview process comes iinto picture once your application has been shortlisted. And for that your IELTS/TOEFL score, Personal statements add value. So if you are in your 2nd year now, you need to figure out the course you want to take up in Imperial College and then prepare for IELTS. The best time to start working on your application process would be once you start your Internship. This is because policies and mode of admissions might change from time to time and it might be too early for you to attempt a Personal Statement or even IELTS. If you start preparing for IELTS from now, you can appear for the exam in your Final year.