Is there something you offer that other salons don't? For example, if you offered a treatment like Shellac, you could write about that. Point out all the benefits, explain who it is most suitable for and make it clear that you are the only person offering it. This means it will be an interesting article that is about something different, whilst also promoting your services.
Try talking to the editor of the magazine about what features have been successful in the past, as they may be able to give you a few pointers.
You could also consider inviting the editor or a writer to try one of your treatments, as a testimonial from them might hold more weight with the reader.
When you start putting the article together, find out what word limit you have. You should have an introduction and a conclusion of roughly one paragraph each. Then decide what main points you want to make in the middle section. Try and plan out each paragraph around those points to help you keep to your word limit. If your article is too long, the editor will cut it down and you could lose some of your best points, so keep it concise and to the point.
Hope that helps a bit. :hug: