Not an instructor, but here's my input anyway.
When teaching anything, the most important thing is that the student is taught the basic fundamentals of the exercise, and that these fundamentals are understood and ingrained in their mind, before moving onto the twiddly bits,
The fundamentals of cross-country flying are :-
1. Dead Reckoning Navigation. i.e with a stopwatch, a compass, a map, whizz-wheel and wind forecast, you can navigate to pretty much anywhere.
2. Time Management during the flight (and the use of mnemonics like FREDA to help with time management)
3. Getting Unlost by reading ground to map (getting unlost using ATC or Nav aids is a twiddly bit for later)
4. Arrivals Planning.
(This is my own hastily thought up list - so add what you feel is missing)
I'm not sure that DR Navigation is demonstrated to PPL students, but I think it should. i.e. the instructor should plan a trip and demonstrate that using map, compass and stopwatch, and a good flight plan, you can go somewhere you have never been before and get there. Then have the student do the same thing, before introducing the time managment aspect.
I've recently revalidated my license, so my recent cross-countries training didn't begin at this very low level, but I think this the right level to start at.