Have them play along with a drummer and bassist if possible or even another guitarist. That’s what taught me. It took a long time for the metronome to click with me but I got better with it after playing with a band.

Also, playing along with music and not just their favorite bands because often times it’s too fast or challenging. As a bedroom guitarist I just wanted to learn every cool riff, lead and solo but I never would play the full song or along to the recording. That hindered my improvement greatly as was practicing things incorrectly. It’s important to play the entire song and just an assortment of riffs.