Just be a decent human being. They are NOT going to ask you medicine based questions to test your medical knowledge. Be yourself and answer as if you are talking to a friend. There are only 2 mmi situations and each with a time limit of 5 minutes. The whole process (from logging on to logging off) took about 30 minutes if I remember correctly. Be a team player, be considerate, don't make assumptions, and be a good friend. I hope this helps! I was very nervous before my mmi as well and am just sharing what I wish I was told before.
They ask us to not talk about specifics from our situations, so i'll refrain from giving details, but the situtions were very similar in style to the Casper exam.