An simple heuristic to use is to go meta periodically, with longer periods between higher meta-level thinking modes.

In this comment nickerst mentions using this heuristic in structured planning:

In my calendar, the habit I've written in is a bit of planning or "meta" time. Twice a week, I plan out a full week. By re-evaluating the course of action half-way through, I'm hoping it should be easier to track where I go off-track.

Once a month, this planning time must include meta-planning. During this time, the idea is to review that my planning method is the most effective. This is the time for reviewing the past month's calendar, and also for reading any books on planning.