To start with, I have not the slightest idea of how mission presidents are trained or oriented now. This is really about how I wish some of them had been given the chance to think thirty years ago.
Day one, for orientation, have them read the essay Pillars of My Faith and then write down three comments they would make to the author. Follow that by reading some comments with approval and explaining that some comments if they were made after training were completed would be cause to send a mission president home.
Then present some case studies of toxic cultures that arose and ask how those reflect on the mission presidents and what do those present think the training needs to include or teach to avoid each of the toxic mission cultures.
Then start normal training after a discussion of fiduciary duty and how it is owed to the elders and sisters a mission president is called to lead and care for.
(All of that said, from other discussions about things people wish were taught in training, I rather expect that this sort of thing is covered -- the things that people have complained about vis a vis other settings and issues actually were taught, people just did not learn. So, this is just a thought exercise, combining ignorance with wishful thinking.).
What would you add to the list for what you would like a mission president called to care for your son or daughter to have been taught? Better, of the things they are taught, what would you like for them to have learned and remember?