My .02: The heck with box placement, as far as safety is concerned. (Yes, of course, show him what the rules require.)
But, if I was going to teach someone how to do any one thing, it would be how to properly strip cable and wires, and how to make safe and secure connections and splices.
That's one thing you really can't learn from a book.
I didn't say that you wouldn't show him how to strip wires, make splices or twist and crimp grounds.
When I mentioned box placement I wasn't even talking about code. For some reason many people don't understand that you just don't nail a box anywhere. I have looked over jobs where they had switch boxes behind doors , they don't use a nailer and keep the box away from door trim. Where the bath receptacle was in the way of mirrors. Learning to do a proper lay out can be harder for people than stripping wires. A kitchen can really be hard for some people to lay out ( they just don't understand placement & planning).
You can't really teach a person to do electrical work in a day but you can show them a lot of little things that will keep them from having to take sheetrock down latter. Even guys that have done commercial may not know how to lay out a house in a functional manner.
Most homeowner tend to leave out lots of things and if you want to save your "friend" some money and help him out then you will make sure that he plans for things like smoke detectors. This may get past the rough inspection and not get picked up until the final. Make sure he gets the circuit for the microwave and includes the exterior receptacles.
The guy has already decided to take responsibility for his own work and that's his decision. Keeping this person from having to take down half the sheetrock in his house is something that I would do for a "Friend".