Sometimes a messy desk results from trying to keep important items visible so they're not out-of-sight and  out-of-mind. Items filed in a cabinet are much more easily forgotten, but visible papers and notes-to-self are reminders of tasks that need to be done.

The trick is to keep the messy area from overwhelming your ability to recognize and find items that need to be completed. Arrange your work space so that your messy area consists of visible piles of paper, each with a cover sheet or a PostIt on top that very briefly lists what needs to be done with that pile.

Now, create an accompanying neat area, so that when you're looking at it, the messy one is out of view, and vice-versa. (This may have been the original inspiration of the invention of the credenza.) You will now be able to turn around to look at your piles to organize and prioritize,and then return to your neat area with a single item to focus on with minimal distraction.