The MMI format is designed to test individuals on their people and critical thinking skills. Therefore, the best way to prepare is by expressing scenarios you've been through in your life - to yourself. The more practice and repetition of the scenarios you go through, the better performance you will have during the live interviews.
When answering questions, you must synthesize the information and develop a synthesis statement. Students who start by answering questions with a restatement of the question are not demonstrating that they understood the question thoroughly.
If the question you’re being asked is “why do you want to be a doctor” and you reply with “hmm, well… I don’t know”. That will not come off too great. You will want to know your exact reasoning for wanting to be a doctor. Make sure you have thought your answer through thoroughly before heading into the MMI.
Make sure you’re also demonstrating empathy in most, if not all, of your answers (if applicable). It is important to put yourself in the shoes of everyone involved in the scenario.