We pre-meds like this idea of having a set list or schedule of things you should and shouldn't do. Ok, so they tell us what classes are required, and that you have to take the MCAT and how many LORs you need. But thats it. Beyond that, nothing is required. There is no magic formula for what you need to do. There are no written rules that you need xxx hours of volunteering, x # of times shadowing, x years of research, x # of publications. Resume building does not directly show motivation. Its been said by many others and I can't stress it enough, do what you want to do, do what intrigues you because thats where you will learn the most and come away with something you can talk about that shows who you really are. Find whats really motivating and stress that. Beyond that, be yourself in your PS. Don't do something just to go through the motions. I'm not saying it won't work to get you in somewhere, but lets be real here, you can't go just through the motions forever. Ok, so you've done some things that interested you, shadowed some doctors in specialities, had some clinical experience, when push comes to shove, put some confidence in your background and experiences. Your experiences make you a better candidate for med school today, show that. Basically through a 500 word PS, a couple secondary essays and maybe an interview you have to translate passion and earnestness. Thats the goal, how are you going to do that? Thats all you need to be concerned with.