I have two MMIs scheduled soon, but haven't had one yet. You want a method of execution, a solid way to approach articulating an answer. But you don't want to rehearse.
I'd suggest practicing every day on a few scenarios, while reading up on bioethics and being familiar with the principle values of the medical field - justice, autonomy, beneficence, non maleficence. Also look into dealing with unethical authority figures, working in a team setting, breaking bad news, and cultural competence.
When you think of scenarios, first identify what the category of the prompt is: ethical dilemma, health policy, standard interview question? Second, identify the problem or issue. Third, identify the the source of the problem or issue. Fourth, think of any relevant life experiences that you have had that apply to this particular scenario. Fifth, find a resolution.
When you articulate it in person to the interviewer, figure out a standard method of approach. Something like:
First 30 seconds, identify what the prompt told you or is asking you to do.
Next 15 seconds, discuss you plan of attack: "I'm going to weigh my two options.." or "I want to identify the pros and cons.."
Then, execute your plan: explore the options, list pros and cons, etc.
Lastly, pick a resolution or option and stick to it.
Leave a few minutes for questions.
That's how I've been doing it.
