Writer Unboxed has an awesome post today about creating a fantastical world and the questions to ask yourself as you embark on this journey.
I am in absolute agreement.
The world in which your story is set must be as real and as vivid as the characters themselves. If the world isn't believable the rest of your story will fail to capture the epic feel that makes a compelling fantasy story.
Your reader wants to live and breathe your fantastical world. After all this is why we read fantasy: To escape into an alternative world, an alternative reality.