First, I clean my room, so my atmosphere feels less cluttered and my mind is less likely to wander of to thinking "I should get around to this."
Then, I'll clean my desk, which usually means throwing everything away that is not 100% absolutely necessary (old notes, ideas, drawings, cups, etc.) These all make you feel crowded mentally and literally. A clean desk lets you focus on the screen without any distractions.
Finally, the desktop. I make a point to zero out my icons when I do this, only leaving My Computer and the Recycle Bin on the desktop, with a wallpaper that reminds me of what my current goal is.
This usually has me inspired to take advantage of the completely fresh atmosphere I've created and tends to be when I create my simplest and most effective work. It also works wonders for coming up with ideas, both creatively and on the business end. Basically, cleanliness helps me solve problems more easily.