Oh, the desktop; such a powerful, yet abused space. It holds any files we need it to. It shows us a pretty picture to help us get in the zone or chill out. Unfortunately, it often gets packed with the most miscellaneous files you could imagine. Your external hard drives might have an icon here. A folder from your last camera card dump. Animated gifs of kittens abound!
But there is hope. Let's take a brief journey to get you to nirvana. As a prerequisite, I would recommend reading The Folder Structure Strong Enough to Carry Your Entire Life first. This article helps you build a folder structure that will take in any sort of file you can throw at it.
Step One - Filing Personal Files
Now that you have some level of organization set up, we can start parsing through the desktop clutter. The first step is to put away all the files that you already know where they belong, but you've been too busy/lazy to do so yet. This probably involves making new folders in your file system to hold them. If you take a lot of photos, you'll likely need to copy those card dumps to your Photos folder (Photos > 2014 > 12-15-2014 Christmas Caroling). If you're a designer, you will have tons of logo designs, lockups and mockups, and image assets. These should all move on over to your Projects folder (Projects > Design > Business Cards or Projects > Apps > Shoutmap). If you make this a habit, you will always know where your latest version of all your projects live.
Step Two - Hiding Programs
That step should have cleared a lot of space, but there's more to be done. Sometimes when programs are installed, they drop an icon right on your desktop. How sweet of them. And how unnecessary. You should delete all the program shortcuts and move any actual programs to your Applications or Program Files folders. There's a much faster and easier way to open programs. On the Mac, just hit command + space then begin typing your program name. Before you're even four letters in, it should start showing your program. Hit return and you're done. The same goes for Windows by just hitting the Windows key and start typing. You may be in the habit of using your taskbar to store all these program icons, but typing out the names actually becomes faster once you're accustomed. This is especially helpful when using a different computer. You don't have to search around for where things are placed; you just type it in and open it right up.
Step Three - Hide the System Default Icons
Now we're getting somewhere. You might even be left with just the system default clutter! Thankfully, there's an easy way to clear these off the desktop as well. On the Mac, with no programs selected, press command + , (comma) to bring up the Finder Preferences. Within here, you can uncheck those boxes to hide your hard disks, DVDs, servers, etc. You can still access all of these within the Finder sidebar, though. In Windows, right-click the desktop and click Personalize, then Change Desktop Icons. From there, you can unselect the icons you don't want to show up (which should be all of them).
Step Four - Polish and Maintain
By now, your desktop should be nearly spotless. If there are still some random files, store them away or trash them! They're not wanted here. Once you're clean, though, you need to stay this way. Get lazy about a few files and your relapse. You can certainly use the space while actively working on a project, but when you get a break, move those files to their real home. They'll be happier there.
There you have it! With a little work, you can sit back and enjoy the view of your clean desktop. It truly does help you focus on work. And your coworkers will admire it.