Think of it like a novel;

Pick a day and just write in a completely separate document. write anything about the world. anything that comes to mind. Think of a good idea? write it down. Just try and get hundreds of words down or even a thousand or two. Spend a different day reading it and adding the parts you really really want into the setting. Flesh out any incoherent thoughts or such. And don't be afraid to throw something out.


And write an adventure first. Build the main details from their starting point. Unless you go big on the adventure they are going to be spending much time in the starting city/kingdom.