What is based on?

---

Your decoration rating is based on the average decoration value of the tiles where your customers stand on.
In build mode you can toggle the decoration overlay (see image) to see where you need to add more decorations.

How to improve?

---

Using the decoration overlay, you can see where you want to add more decoration (ideally you don't want any red/grey tiles in your store).
You can improve your decoration value by placing decorations like plants, fountains or posters. Certain types of flooring also have a positive impact on your decoration value.

! Only the tiles where your customers stand on have an impact on your decoration rating. So having all your decoration away from your customers will not help your ratings and you don't need to improve your decoration ratings in areas where you don't have customers walking around.