I’ve had occasion to “break in” a couple new sound people.
The thing I found really effective was to give them the boom and mixer, have them put the headphones on, and then walk around while talking to them, having them follow me while listening carefully to what they were picking up. It also forces them to be aware of their surroundings and their personal safety, as I did this in parks, with uneven ground, trees, and the Mississippi River nearby.
I’d tell them what to listen for, from extraneous ambient sound to “cable slap” inside the boom, and also continually remind them of not tripping over anything – while randomly changing speed and direction as I walked.
It worked.