I find that if I base the overall world around something I dislike the rest falls in place. Like the war in Iraq, so I would have a mountainous terrain with a dictorical ruler, and then I would base the plot around that.
That is excellent advice, Gorgon. Take heed at what he's saying there, MoD. Outkast's method works too--but, the problem with that is that people who work that way often get 'worldbuilder's disease.' Or, in layman’s terms, too much time spent worldbuilding, too little time spent plotting.
Before you begin, I think you should decide how big your story is. Is it an epic? If so, you'll need more world to make it feel right. What is the conflict? Gorgon's method is a good one because it helps you focus your details on areas of interest--areas of the world that will cause conflict.
You also have to decide how much worldbuilding is your focus. Tolkien loved to worldbuild--that was his reason for writing, was to better flesh out his world. That's fine if you have a decade to tell your story. However, I see many newer authors spending ridiculous amounts of time crafting their worlds, and then when they actually write, the worldbuidling feels weak because they didn't focus enough on the areas that will be important to the plot and characters.