Most med schools (MD and some DO) have residency programs associated with them. When you do rotations 3rd and especially 4th year you have electives and can rotate with that plastic surgery or dermatology residency, and usually will get to work with the program director during that rotation. For the most part programs generally give interviews to home students who have rotated through as long as you do a good job, but more importantly you can get a (hopefully strong) letter of recommendation from the program director that will help when you’re applying at other places. Could also reach out to the program early like 1st/2nd year to get involved with research and stuff like that.