One of the things you find is that different people need different areas that need more work than others. One pilot may have scan issues of not understanding the relationship of the "replacement" instruments. Another might have control problems during turns. A third might have trouble with the simple math of knowing how many degrees there are between the current heading and the new one.

After an overview on the ground on the basis - replacement instruments, scan techniques (which should be related to the student's full panel scan), the role of the mag compass - I'd just go fly and keep a close lookout for the problem areas in flight and do a full debrief on the ground to get the student's own impressions of where he found the most trouble. And find ways of overcoming those issues.

BTW for the scan/mag compass issue, I've found it a good technique in an early lesson to cover or fail the mag compass for a substantial period of straight flight, both level and with climbs and descents. The idea is to give the student confidence that if he keeps the wings and ball level in the TC, the airplane will tend to remain on heading and that he can indeed fly with it instead of the AI.

And, please, don't allow the student who is good at this to come to the conclusion that partial panel is not an emergency.