I built my first ever skill. What I built: a skill that drafts my invoices and letters of agreement. This is admin I repeat for every single client, so instead of rebuilding the same documents from scratch each time, I turned the whole process into a skill. Now I just tell Claude something like "draft an invoice for [client] [amount], [scope]" and it triggers automatically, pulls in my agency details, payment terms and currency, and hands me a clean, ready-to-send document. Same for a letter of agreement. One optimization: watching it run the first time, I noticed it kept asking me for the same details I use on every doc my business info, banking details, payment terms. So I baked those straight into the SKILL.md as fixed context and will keep reiterating, as the lesson mentioned, the more you use the skill, the more you can improve it and the more you can get better. That's very, very important. Now it stops asking and fills them in automatically, and only asks me what's actually different per client. First pass is right almost every time now. The lesson that clicked: a good skill isn't about the AI being clever it's about front-loading everything you already know so you never repeat yourself. A 10-20-minute admin job is now about 30 seconds.