You know stuff. Yes, you do. It is highly likely that you have specific knowledge of something that would be of interest to someone else.
The first step for How To Put Up a Workshop: what do you know? It took me years to realize that while I am a character driven writer just like a bunch of other writers, I have a whole actor's toolbox at my back when it comes to handling characters - a toolbox I could open up and offer to other writers. Insta-workshop. A good friend is fascinated by the novel Peter Pan by J.M. Barrie. She has turned into the ultimate research geek for Edwardian fashion, manners, and ships/shipbuilding - not to mention her depth of insight into a single piece of literature. She has all kinds of workshop opportunities there. (Costuming/fashion, research resources for the time period, etc) Maybe you have a job you often see depicted inaccurately in fiction. There's your workshop. Or you have in depth insight into the mind of a serial killer because you've never, up until this very workshop, confessed that you are a serial killer. Whatever your knowledge, someone, somewhere needs it.
Second step for How To Put Up a Workshop: can you communicate your special thing in layman's terms? Part of the challenge of knowing what you know is that you know it. You take what you know for granted. Teasing apart what you know so that it's accessible to others is no easy feat. Solicit feedback from someone outside of your specialty field. A critique group can help. Or friends who know nothing about your deep, dark secret life. If it's the serial killer thing? I can't help. I'm busy.
Third step for How To Put Up a Workshop: pick your audience. Serial killer? I suggest that law enforcement might not be your ideal audience. The rest of you may have noticed I like cats. Hanging out with the cat fancy, I can say I have picked up a fair bit of information about the genetics of feline coloration. Specialized knowledge that's utterly useless to just about everyone else on earth. Knowing that my workshop audience(s) are likely to either be writers or steampunk enthusiasts, I have to realize nobody else cares that genetically speaking there's no such thing as a brown and white tabby cat. Unless I'm making a point of coming up with a mad scientist aboard and airship somewhere who's doing the impossible with gene splicing brown and white cats with machine components. Your audience is likely going to be determined by the conferences and meetings you already attend. Most of us are going to develop workshops for writers or for readers. But what other events do you attend? Our marina brings in speakers on subjects specific to boaters - crossing the Atlantic, managing storms at sea, circumnavigating Vancouver Island or cruising the canals of France. . .match what you know with who might be intrigued by what you know. Check your local libraries. Don't limit your audience. What you know may be applicable more than one place, which brings us to:
Fourth step for How To Put Up a Workshop: develop for more than one format. If you belong to RWA, you have amazing opportunities for putting on your workshop in multiple formats. You can teach your workshop online via a series of lessons you write out and then interactive emails with participants. Do this through your online chapters. You can present your workshop at your local chapter meeting. You can submit your workshop proposal to a local conference. Last but not least, you can submit your proposal to the National conference.
NOTE: while I echo the advice that interactive workshops are really helpful, don't think you'll get people out of their chairs to participate in actual movement once you reach local and national conference levels - everyone is in nice clothes and shoes. Interactive at that point means getting workshop participants to talk to you and/or share writing.