The background of the protagonists is pretty much different, but in some ways, the heroines are quite similar.
Both are young girls, who change into older forms to become idols.
Both have a somewhat chaotic manager.
Both have a rival in their idol form, who is on good terms with the younger incarnation (more extreme in Full Moon, where Madoka regards the protagonist as both best friend and biggest enemy)
Both have 2 magic companions, male and female (animals in Creamy Mami, with animal features in Full Moon)
So if you watched Full Moon and you are looking for a similar hero in a more light hearted setting, you may go for Creamy Mami. Or, coming from Creamy Mami, you can go for Full Moon, for a more melancholic story.