I am a 2nd year undergraduate student. What should I do now to prepare for my PhD?
As an undergraduate student, the best thing you can do to help your admissions case is to get involved in research. This will allow you to demonstrate that you have the capability to do good research, which is one of the biggest things admissions committees and individual professors are looking for when choosing among applicants. Maintaining a solid academic record is also useful, and having an understanding of the literature in the field you're interested in is also good. However, direct experience will let you see if academia really is what you want to do or not.