As a former Cadet and member of the Reg Force, I think I can answer this for you.
When I was in the Militia, I was asked to instruct some of the local cadets in the art of patrolling in order to prepare them for a patrolling competition. Part of this was Cam and Concealment. They won the comp.
What I did was to get available films on the subject, write a lesson plan using the fieldcraft manual as a reference to explain all the basics, and I set up a field plan for training.
I gave the lesson, showed the film and asked for any questions.
In the field I demonstrated proper cam and also showed the difference of improper cam.
I then used staff to demonstrate un-cammed in tree lines/bushes and then cammed in tree lines/bushes. You need to show the difference. I also demonstrated bare skin in bushes, sleeves rolled up, etc. Use your imagination.
I then had the students practice camming up and checking them,
Then I had them hide in a bushy field and lined up the staff to see if we could spot them, then we walked through the field to find those we couldn't spot right off the bat. Those that didn't get picked up were rewarded. Make it a competition, they love it.