Buy fabric that is large enough to cover the surface of the box. Be sure there is enough drop-off to fit around the corners of the box.
Place the box on top of the fabric, right-side of the fabric facing away from the box. Start with one side and pull the fabric tight against the box. Fold the fabric under to create a hem for a more finished look. Use a staple gun if you have a sturdy box that will support staples. Glue the fabric onto the box with a glue gun if the box is too thin for staples.
Wrap the opposite side next, using the same process. Fold the corners of the next side so it looks like a wrapped package and secure the fabric to the box. Finish the fourth side, making sure that the pattern of the fabric is even and not warped.
Add a decorative trim such as ribbon or a strand of lace to give your edges a finished look and to incorporate another decorative element.