Your workshop will take your chosen learner from one level of ability to another. It’s important to make sure that this leap is big enough that your workshop acts as a valuable resource and a source of inspiration, but is small enough to be taught in 3-5 practical sessions (unless you’re planning a longer-term course).
It’s also important to think about your workshop progressing in difficulty as a steady rate, so that the learner feels challenged but isn’t overwhelmed.
Take a look at your chosen skill(s) and make a list of all the topics you could cover in your workshop(s). Next, think about what will motivate your chosen learner and cross out the topics that are less essential; the topics you think might go beyond the scope of your first workshop.
You should be left with a short list of topics that stay within the scope of a more broad subject matter.