I have found that when I really read fantasy, my prefered genre, it makes the mind more able to turn the appropriate phrases. It is like immersing yourself in a culture to learn the language. And you can fine tune this effect by reading specific sub-genres or series. Say for example you want to write humorous fantasy, you might read Xanth novels, the Myth series by Aspirin, or even Discworld novels. I think such reading is most helpful. It jumpstarts the brain.