Shaddowing is a good idea - to make sure you like derm enough and to make some connections to help you later. Even if you just spend a little time on it, that would be a good start. Also, ask around your derm department about research projects, or even just case reports to help write up. These are things that can boost your application.
Board scores seem to be the most important factor, with grades next. However, we all know of someone with awesome boards scores, aoa, who didn't match derm (i know of more than one person who fits that), so start working on the research and getting to know people in the derm department now and let them know you are interested early and consistently. It's a super-competetive specialty, so do everything you can.
The good news is I know someone who matched derm with average board scores, barely top half of the class grades who match b/c he made himself well know to the derm department by going to departmental conferences, shaddowing doctors, writing up a few papers. So it can be done.
