I've never done a med school interview before, but here are some tips from being an executive who was the decision maker on the other hand.
1. Research the medical school. Yes, you've probably done this when writing secondaries but do so again - this time more in depth. Know their mission, as if were tattooed on your head, and be able to refer to it with ease and connect it to your experiences, who you are, and why/how you will support their mission as a student and graduate.
2. If you are given the information, research who will be interviewing you. Gain as much info as you can - know their hobbies, interests, where they went to school, what they've done since school, recent publications or EC efforts and formulate questions regarding them. For instance, I saw that you went to X school and are now faculty at Y. From your experience, what differences do you enjoy at Y vs at X? Or, I read your paper(s) on (fill in the blank) and understood the idea(s) of (blank) - how did you arrive at this focus of study and are you in what capacity are you continuing the work? Are there opportunities for such things? Or, I saw there is a clinic here for "blah" and one of my most impactful experiences was working with said population - what opportunities are there for students to support this mission?
3. Basic decorum: Dress appropriate. Use good grooming hygiene standards. 15 min early is on time - any time afterwards is late. Everyone you meet is sir, ma'am, or doctor - unless told otherwise. Stand up tall, look people in the eye, smile, shake hands firmly. Leave your electronic devices preferably in another country, but if not the car works well, too. There is a grand total of zero reasons why you should be seen staring at a screen at any interview - ever.
