1. You know how the world is run. (There has to be some sort of government).
2. You know who are the powerful and who are the downtrodden (some things are just universal!).
3. You know the immediate setting for your story intimately. You need to be able to portray this, almost as if it were a character in its own right.
4. You know where your characters fit into your world (and whether they fit in well or not. Do they defy convention or follow it religiously?).
5. You have some idea of how your people survive in terms of food/water/sanitation/employment provision. I can't think of any created world where characters don't have to eat, be able to resource themselves etc.
Not all of these details need to make it into your story. We don't need to know everything about politics in your world but we do need to know what matters to the story (which I think is going to be a new mantra for me but it is a useful one!).