I'll add my two cents on the matter.
First, for every interview question I would come up with a couple talking points that I made sure I hit when practicing (like 3 bullet points each-ish). This is not a script, just a general idea of how my answer should flow.
I also am very shy, so one thing I did that I think helped was to literally strike up conversations with strangers (on a train, on a plane etc.) where you are going to be next to them for a while, and I would try to talk about my med school dreams. If you can't explain to a 65 year old grandmother why you want to become a doctor while sitting next to her on a plane to New York, you sure as heck can't explain it during an interview.
The best advice I could give to gain social skills would be to go talk to girls at bars. Every nervous little twitch you have will come out, and you yourself will notice it if you aren't keeping eye contact. Often bars are loud so you really need to pronounce words and inflections correctly, which makes you slow down and try to be clear. Through this method I figured out that I did this really weird thing where when I get super nervous I quickly look and move my head to a side and then look back, and girls would legit call me out after I would do it 2-3 times, which made me figure out that I did it so I could fix it.
