Today's exercise is to expand on one area of the culture you've created for your world. We have a bare-bones timeline, the bare-bones elements of a language, the bare-bones of an economic and political scene. Today, select one of these areas to flesh out. If you're writing a novel with a more political plotline, flesh out the politics and economics. If you're writing something really "alien" in feel, or if you're writing high fantasy, flesh out the languages. If you're writing a story whose plot hinges on the past, fill in your timeline (probably not needed if this novel is a sequel, though).
Write a complete timeline for your setting (last 500 years or so should do, unless your characters are long-lived or major forces earlier than that are truly world-shaking) and for your protagonist's life up until the novel opens. Make notes on how these forces will later impact the story (ex: Expansionism one hundred years ago is going to lead now to revolt in the Islands; the hero lives there and is going to get caught up in the revolution).
Write a 1-paragraph description of each major political body (churches, governments, kingdoms, factions, economic forces, guilds, etc.) and name them now so you can refer to them as needed later. If you want, take extra time and write one sentence about how 3 of your groups (the 3 most important groups) feel about all the other groups.
Names and Language:
Write a short glossary or lexicon for some common or important words (like rock, bird, horse, king, ford, river, stream, mountain, holding, village, magic, outsider, etc.) These can be combined and declined to make place names as well as surnames and even first names. Write down five place names and five character names that you can use when you need them. If you want, take extra time and fill out your map with appropriate place names now.