Notice what made the task work
Which inputs mattered? What checks caught mistakes? What required judgment? Those are the ingredients worth preserving in a skill.
Keep the skill focused
Write one reusable process for one type of task. Include when to use it, what it needs, and when it should ask for help.
Test it with a different example
A method that only works on its original input may be too narrow. Review another run before making the skill part of a routine.