My best areas (I think) are inspired by a root "storyline" or quest that feeds the imagination when area building. For example, I recently wrote an area based on "Alice in Wonderland and Dorothy in Oz meet Timothy Leary". I wanted an evil witch, a quest to defeat the evil witch, and a quest to help the evil witch. From here, I knew the witch needed her minions, and that led to a sub-area where her minions came from. I needed a princess to rescue and this led to creating a prison for the princess, and a sub-area to find the knight that would free her. I needed a quest for which the princess would defeat the witch, so that led to 3 sub-areas where the quest items would be found. You get the idea.

The end result was a whimsical land that players seem to enjoy, a lot of mobs to bash if that's what they're into, lots of quests (about a dozen) for those that like questing, and a land where everything is interconnected through a storyline.