So in your fictional world who are the main inhabitants of that world? Do they accept the existence of life outside of what they know? Do they attempt to make contact at all? Are they successful? What are the consequences?
How do they make contact? Is magic involved? And what happens when a magical species meets a non-magical one? How can the latter survive without any obvious defence against magic? Do they persecute those who are magical to try to protect themselves?
And if your world was originally inhabited by a species that was driven out, how did that happen? And what would happen if that species tried to come back?