The instructions should remain understandable after the expert has gone home.

Instructions written by someone who knows a system tend to omit exactly what a newcomer needs, because those parts have stopped looking like steps. Assumed knowledge is invisible from the inside, and the gaps are always in the places the writer finds obvious. The real test is not whether the expert can follow them. It is whether someone else can, on a bad day, with nobody available to ask.

Hand the instructions to a person who has never done the task and watch without helping. Every hesitation marks a missing line. Add those, and define the specialist words where they first appear.