The thing that helps me do a good job is that I don't feel the need to explain everything about the world to my reader. I'm not writing a history text on the Four Corners. I'm telling a story that's set there. The setting belongs in the background for the most part, and it's easy for fantasy authors to forget that. That's one of the unfortunate parts of Tolkien's legacy, in my opinion. Read the first hundred pages of the Fellowship of the Ring and you start to get pissed, "Shut up about the Shire's museums! Isn't the world supposed to be in peril or something?"