For a yoga business, newsletters are a great way to stay connected with your group of students. Once a month or every other month I believe is sufficient if you have some valuable information. It is useful for sharing upcoming events as well as inspiring stories of how yoga has impacted someone's life. One of the newsletters I receive includes a short sequence of poses for a specific purpose, such as easing low back pain. Another newsletter I subscribe to also includes a couple delicious recipes relevant to the season or holiday.
I think my students would enjoy information about the origin or purpose of some the poses we do as well as inspirational quotes or stories that uplift the spirit. They also enjoy jokes or funny stories having to do with cats and yoga. Information on anatomy and how different poses affect the body might also be interesting. Tips on staying healthy or losing weight are generally very popular topics as well. The key is short, sweet and to the point so they look forward to the next one.