I had a nice long answer all typed out, but the computer decided to eat it.
I'm working on a set of plans for teaching a CFI Applicants. Don't anyone hold your breath for these as the ETA is 2-3 successful CFI Applicants first.
Briefly, for teaching CFI Applicants, we started with the Table of Contents for the FOI. There is a lot of good stuff in there that the Jepp & others seem to really gloss over, skip, or outright ignore. For instance, we spend time discussing the affective component of learning and why a student that is beating themselves up tends to make more and more mistakes.
Next, we get into the individual topics (PTS Tasks & Special Emphasis Items), where we discuss a particular item from the commercial or private PTS (and make sure they're updated!), have the CFI Applicant create their lesson plan however they are going to do so (bought, created, whatever works for them), and then the CFI presents that topic. The audience gradually moves from guiding to displaying the common errors. In-flight, as the CFI Applicant becomes more comfortable conducting maneuvers from the right seat, explaining those maneuvers while doing them, then eventually teaching those maneuvers and correcting the "student" mistakes as the CFI teaching the CFI Applicant demonstrates the various common errors. We spend extra time on areas where CFIs get themselves into trouble (slow flight, stalls, pattern-work) and treat every lesson as a scenario, though at first only a few minutes are spent on that scenario.
There is really only one way to become competent at teaching CFI Applicants, and that is to teach CFI Applicants, preferably with an experienced CFI and/or DPE that can serve as a mentor while doing so. No one has been born knowing how to produce competent, safe, and effective CFIs, thus it is a skill that must be learned.