The short answer
Write a rule when a mistake repeats, is expensive to fix, or reveals a check that the next person or AI assistant can reliably perform. State when the rule applies, which source governs the work, what to do, and how to verify completion. Test it in later work and revise it if it conflicts with better guidance. A one-off wording preference may need only an edit to the draft.
A closer look
A useful rule prevents a class of mistakes rather than memorializing every correction. If AI repeatedly changes the wrong file, invents a missing fact, or claims completion without checking the live result, turn the lesson into a source rule, checklist item, or approval gate. Give the rule a clear trigger and a way to prove it was followed.
Rules also require maintenance. If a new instruction contradicts an older one, decide which source has authority and remove the stale direction. The point is to make the next project easier and safer, not to make a simple task carry an ever-growing manual.
Use the guide to writing an AI task brief to give the next task a clear boundary and completion check instead of adding a vague new rule.
