It really depends on you and what your needs are. What specialty are you looking at? How are your grades? How good a test taker are you? What kind of research are you thinking about doing?
General advice: boards and grades before all else. They aren't the MOST important thing, but they are the FIRST thing that gets looked at. If they suck, nobody will ever see your research. If you know yourself and are sure you can do well with those and nurse along some little project(s) on the side, then by all means do a little research. Find something easy and not too terribly time consuming. If you're not sure, then focus on grades/boards right now and do research during M3. It's harder to balance time-wise, but you can usually bang out some case reports or some smaller retrospective database stuff on weekends.
If you have an idea of a competitive specialty you'd like to do, you need to start having some sit downs with advisors in that department. Find out which attendings are good student mentors and advocates and put yourself in front of them. This is something you definitely can do right now. Get their advice. It will be much more valuable because they will know you, know your school, and know how students there typically do matching your desired field. They will be able to give you some good advice and get you plugged in with the right people.
Good luck!
