Here are some ways to get your stars higher!
have atleast 2 vets and 2 grooms (more if you have a lot of boxes...)
gert carrots (it atracts more poeple!)
set your price as 10-12 dallars or no one is going to come!
get fertile meadows
get straw or flax bedding
get 16 square meter boxes
have atleast one 18 square meter box
get a large fertile meadow
get a greenhouse
If your ec becomes more popular raise the skill level of the horses a bit or the price!
I hope this helped! If you have anything else to add to this list please tell!