Pick the right thing before you write a single line. Most failed skills started with the wrong target.
Before you write anything else. No instructions, no examples, no setup. Just the question: what task is this actually for?
Which task do you (or your team) repeat more than twice a month, where the output should be the same kind of good every time?
Explaining the task to a new hire takes more than ten minutes. You catch yourself saying "let me show you how I do it" again and again.
One-off task. Highly creative work that needs a different angle every time. Decisions that change weekly. Don't force a skill on these.
From my own setup, ranked from highest hit-rate to most niche:
Use the skill-creator skill. Step 1: identify the task. Ask me what I actually repeat more than twice a month. Then help me finish one sentence: "This skill does ___" — in twelve words or less.
If skill-creator is not active yet, see the setup on the Skills start page.
Write down: "This skill does X." If you cannot finish that sentence in twelve words, you have not found the task yet. Keep looking.