Clean out your armoire. Remove all of its contents, then dust and wipe down all surfaces. Move the armoire to its new location in your home. Because you can close the armoire up completely to hide your desk's clutter, you can tuck it into just about unused space in a kitchen, bedroom, guest room, dining room or living room without spoiling the original look and function of the room.
Install a pull-out keyboard tray under the main shelf -- this is the shelf that your TV formerly sat on. Most TV armoires will easily accommodate a pull-out tray; however, measure first to make sure that the tray's width will fit under the shelf. Measure, also, to make sure that the tray will not be so low that you cannot comfortably sit in a chair pulled up to it. In other words, when pulled out, the tray should be high enough from the floor that it does not bump your knees when you are sitting at your desk.
Follow the tray manufacturer's instructions to install it. This most likely includes installing glides or brackets by drilling holes into the armoire's shelf, then connecting the tray pieces to the armoire with screws.
Set up your computer's hard drive and printer on the bottom shelves. If your armoire has a built-in electrical outlet or surge protector, you can plug them in there. If not, you may be able to access a wall outlet through a hole already in the back of the armoire. If your armoire does not have an access hole, carefully cut one in an inconspicuous place on the back panel.
Set up your computer's monitor on the main shelf, and the keyboard on the pull-out shelf. Add a small desk lamp on the main shelf, if desired.
Fill empty shelves and cubbies with desk accessories, such as printer paper, computer media, a stapler and staples, pens and pencils, a calculator, scissors, envelopes and stamps. If your armoire is not equipped with cubbies and multiple shelves, fill baskets, stackable bins or boxes with these items and store them on the shelves. Set aside a cubby for bills and mail. Place a small wastebasket on one of the lower shelves.
Hang a magnetic dry-erase board on the inside of one door, and a cork board on the other. You'll have not one but two handy spots for jotting down notes and tacking up reminders.