Pretty much whatever you learn, teach them. I'm going out of town for 2 weeks (super nervous!) and teaching my tank sitter every little detail. How to correct temp swings, test salinity, test other parameters, what should everything look like healthy? What are first signs of something wrong/stressed fish. What if the skimmer pump gets jammed? Do they know how to take it apart and clean it? How to do emergency water changes if needed and everything that goes along with that.
I think you get the point, pretty much the more you teach them...the better of you'll be.