I think you have two different audiences you are targeting and they will likely require different approaches. I agree that an up-to-date website is important as well as a FB page that is “active” with current pictures and information. In my area our local FB group is where “horse people” go to get recommendations for boarding, training, lessons, etc. If you have a local horse group page, or even one for your state, I’d start posting on there announcing stall openings, lessons, etc. This will get (and keep) your name out there. To attract beginner riders you may have to go a different advertising route because those people may not be familiar with the local horse community resources. Definitely put fliers up in your local tack shops, feed stores, etc. I’d also post on local FB pages that are not necessarily horse related, but geared toward your general area and/or kids activities in your area. If there is a “mom” group, or maybe there is a “online garage sale” type page or even just a city/town type generic FB page (my area has one that people post about new restaurants, or asking for things to do with their kids, etc).