Join EMRA as a med student member. It's only something like $40/year for med students and it give you access to lots of interesting and useful stuff (med student survival guide, med student pearls, med student-resident mentoring program etc). Also, I think (and others can say yay or nay) it shows that you've got a strong interest in EM since you're joining a professional society in your chosen specialty when you're still a medical student.
After you get settled into med school (the first semester you're basically figuring out how to study for med school), go to the EM department and see if there are any research projects that you could jump in on. Also try to see if there's someone who would let you shadow them for a shift whenever you have free time.
Go to one of the national meetings. I'd say if you can only go to one, go to the Medical Student Symposium at SAEM in May of your third year of medical school. The reason why that one is (IMHO) the more important one is because in May the PDs are done with the stress of the previous year's Match and they haven't started with the stress of the next (your) Match, so they have both the time and the interest to talk to you. Also, if you go to the one at the end of your third year, you can check out the programs that you're interested in and introduce yourself to those PDs (especially the ones you've scheduled externships at).
Try to do as well as you can your first two years, but don't stress too hard over it. If you're going to stress over anything during your first two years, stress over step 1 because it's the most important thing in your first two years. That being said, I think it's less important in comparison to other factors (SLORs, third year shelf grades, the interview, etc.) Others with more knowledge can comment on that one.
Good luck! I'm sure you'll do just fine!
