In order to maintain a clean desk you have to restrict the number of objects. In order to get used to having a clean desk I recommend to start with the following minimum only:
- Network connectivity
- PC / Laptop
- Pens in not more than three colors
- Clear folders
On top of this you are allowed to have only one other thing on the table, which are documents related to the subject you are working on just in this moment.
I also recommend removing all personal objects from your table. Only when you became an experienced clear desk practiotioner you might consider bringing back som decoration.