Meet as many people as possible and let them know you are a writer with skills to create writing workshops. Show them some of your work. Give out fliers. Go to schools and fairs. The more people you know, the more likely it will be to create the right writing workshop
Make sure you are knowledgeable in your topic before you decide on it. Try looking up similar workshops and create a systematic program for your workshop.
Remember to set long and short term goals for your workshop. This can be personal and professional goals as well as those you want for your students. Buy materials which will help you achieve those goals.
Make a list of everybody you know who might be interested. Get the word out in your peer communities. Ask friends to pass the word, and start discussions casually about it with people when possible.
Look for the right venue. Try to find a central location which people can easily get to and can be seen in town. Look into free venues such as churches, town halls and university campuses. Establishing a good repertoire with these people will only increase your networking.
Start publicizing the event. Try to place fliers and brochures wherever you go. Expect that for every ten people you invite, one might show up. Bear in mind not all the people who show up will be constant, but show your appreciation for the ones that come.