I've seen this discussed before on a message board, but I can't find the thread. The question was this: when getting ready for the game, do you (a) draw a map first and then key it, (b) draw the map and the key at the same time working as you go, or (c) write some sort of key (such as a roster of monsters and traps) before building the map to suit? This also begs another question, that of the backstory. In general, unless it's a funhouse type of dungeon, there's a backstory -- whether or not it's ever revealed to the players, some sort of idea usually unifies the encounters even in a location-based adventure.
What's the order in which you mentally organize, prioritize, and develop your adventures?