Details that are believable (and appropriate for that world). Outlandish is fine as long as that has been established as a major characteristic and not just "thrown in" at the reader.
Differing groups, each one with unique qualities and habits, and how these interact within their own group and with the others.
A sense of how the world is now at the state that it is (did historical battles have an effect? In my fairy kingdom, past battles have made certain areas barren as nothing can stand having too much magic go through it. This conjures (ahem - pun alert!) up images of barrenness, gives a sense of history and that there is rivalry between differing groups as realistically there would be.