You're smart. You know lots of words and you have more concepts and ideas in your head than most people. But, you may need some help on knowing what a desk is...and is not. This article is about what a desk is NOT. Be sure to read the other one I have on what a desk IS. As a professor, you need to be clear that a desk is NOT

1. A storage unit. Look at your desk right now. If there are items that have been on your desk for longer than a few days (or even a week), then you're treating your desk as a storage unit.
2. A book shelf. Do you have books either stacked on your desk, or maybe even in a tidy row with bookends? Either way, a desk is not a bookshelf, so move those books over to your book shelf.
3. An in-box. If everything that comes into your office goes onto your desk (or the chair that is right next to your desk and serves as a desk extension of sorts), then you are using your desk as an in-box. Not good. Get an in-box to put ON your desk...but wait, that's a whole different article so I won't get started on that here.
4. A permanent repository. Besides the top of your desk, you need to consider the inside drawers. The vast majority of folks have items in one or more of their desk drawers that have been there a REALLY long time. Desks aren't meant as permanent repositories for anything.
5. A photo album. Sure it's nice to have pictures of a pet, a family member, a great view, the coolest thing you ever found in your lab, or any other memento to look at. But, not on your desk. Put those pictures onto nearby shelves or on top of a file cabinet (and do you see the assumption I'm making, i.e., that you have room on a shelf or file cabinet). Whatever the case, move those pictures off your desk. A desk is not a photo album.
6. A museum. If you are an artist, an archaeologist, an historian, or any other academic who finds and treasures nifty items, that's great. however, your desk is not the place for this trove to be displayed (or stored). A desk is not a museum.
7. A pantry. One or two food bars, hot chocolate packets, or Ramen Noodles is OK, but when you have entire drawers dedicated to the storage of food, then you're not using your desk for its intended purpose.
8. A pharmacy. If your drawer has enough analgesics, antacids, lotions, potions, and powder to stock an aisle at your local drugstore, then it's time to do some tossing (and/or to get some medical attention!)
9. A holding zone. What is just sitting there...waiting? It might be something you're waiting to file, waiting to hear back on, waiting to see if you're going to move forward on it, waiting until the next time you teach this class, etc. Whatever it is, move it to a home that is somewhere other than your desk. Your desk isn't the cell-phone waiting area at the airport. It's a place where you can do some work without undue clutter and distraction and 'holding zone' items are both.
10. A supply closet. Depending on how long you've been in the professoriate, you've been through the inevitable ups and downs of the economy and the ebb and flow of the department budget. Sometimes, you know when times are good, you better stock up. Not necessarily a bad plan, but the place to store all these excess supplies is NOT your desk. A few pens, some paper, a pad or two, as well as a reasonable portion of other office supplies is OK to have handy in your desk. But if it's more than you access in a week, then it needs to be somewhere else. Somewhere like an actual supply closet.