This collection contains pointers to a variety of ready-made promotional materials, such as posters, flyers, and brochures. Some are generic, some are more specific to a club or dance. Some are in an editable form, others are PDF or image. All can be mined for ideas.
The British Columbia Square and Round Dance Federation has accumulated a good collection of promotional materials at this site. It includes a wide range of material such as: articles, social media posts, videos, posters, brochures, and images.
The article addressed by the link above shows the full list of entries from the MCASD Toolbox (Metropolitan Chicago Area Square Dance) collection. The ones specifically providing providing posters, brochures, etc. are: