If you need to do better at your next medical interview, it is critical that you focus on three main areas.
You need to produce structured answers. Try to establish what kind of structure you want to deliver your answer within, before you begin talking.
Remember that basic communication principle of telling them what you want to tell them, prior to telling them your message. Then tell that what you told them after you have told them your key items.
Finally, remember to sell yourself within every answer to every question. The interview is essentially a sales pitch in which you are the product as well as the sales person.
This can feel uncomfortable, but it is something that you need to do in order to improve your chances of success.