I'd never really heard of Stack Exchange before, but there is apparently an RPG board there that offers ranked advice on problems that people have. On someone's question about 'How to create a D&D setting,' RPG blog mainstay Kelvin Green has some great advice to offer on the topic:
What I would not do:
Try to create a campaign setting.
What I would do:
Make a list of all the ideas and concepts I want to use in the setting. Put the list away and go and make a cup of tea. Go through the list and make connections between the items. Leave all the dangly bits, because I'll find ways to connect them later.
That's it. Really. You don't want to try to create the whole thing from scratch or, and this is important, it will never happen. Start small, start with a bunch of ideas, build outward as the game goes on. Ideas will occur in play which would never have done so beforehand, and best of all, the players will come up with ideas that you can pinch and include.I like this. I like this a lot.
I've never been able to craft sandbox rumors or the economy of a fantasy city because, ultimately, I really don't care about that stuff. But what I do like are stupid ideas to make things fun. I can make everything else in the world bog-standard default D&D for the sake of my sanity and free time, but throw in a handful of fun little tweaks to keep things fresh and unique.
So I've made a list and I've had a cup of tea. Some of my list covers overarching campaign ideas, some cover new monsters and magic items and some are just fun little setting bits. I'll start putting up posts on them today.