I'm nowhere near done with my own campaign-building, but maybe sharing what I've done so far will help out the original poster or perhaps someone'll give me some guidance.
I started with coming up with an odd element-based calendar system. To be a bit different, I didn't use a standard set of elements- I came up with five whose meanings are a bit more metaphorical than a standard set. That sort of inspired me with some cool ideas about history, magic, religion, non-human races and such through an emphasis on the elements and their number. Continuation of some of those things gave me ideas for adventures. I suppose that's as far as I can help- ideas build off each other and are connected, perhaps in ways that aren't obvious.
My problem is getting about that far and hitting a brick wall. Those cool ideas were too much to graft into an existing setting, but not enough to be a full world. (I don't really know very much about politics, organizations, recent history, technology, daily life, geography, etc.) And without all the nitty-gritty, I don't have enough to actually do stuff, contrary to my previous beliefs. (I was having problems spending points and coming up with disads earlier, but seeing how much of many characters is world-specific, knowing more about the world would be useful) Anyone have any advice?