It is time to clean off your desk because you can no longer find what you need. Remove all items except computer and printer if you have a large enough desk to accommodate it. If your computer is a laptop, put it in position so you can easily use it. If it is the keyboard and monitor, place the keyboard on the keyboard drawer (if one exists) and the monitor in a location you can easily see and you are not straining your eyes or neck.
Next, put back the items you use frequently such as your stapler, tape, writing utensil holder, in/out basket, or any item used to hold folders. Once those items are on your desk it is time to start with the paper, which can be overwhelming. Toss all the papers that have been dealt with and you no longer need. Also toss old ads, coupons you forgot to use, invitations and thank you notes no longer relevant and scraps with old numbers and notes. If the paper has been on your desk for weeks or months and you still have not done anything with it, maybe tossing the paper is your best option. Many times clutter is just delayed decision making. File those papers you really need to keep. Or if you are reducing your paper, considering scanning them but remember to back up those files.
Once you have dealt with the paper, look at what is left and make the decision whether they are really needed on your desk or needed at all. Remember schedule filing and cleaning your desk on a regular basis so your desk stays clear.