One way to decorate a shoebox for Valentine's Day is to turn it into a mailbox to hold cards. Cover the lid and the main portion of the shoebox with construction paper separately, so that the lid can be removed later. Cut a horizontal slit on the short side of the main portion of the box. Decorate the box with pictures, letters and words cut from old magazines.
Another way to decorate a shoebox is to use masking tape to secure the lid to the box. Use a ruler as a guide to cut a large enough slit in the lid to reach in and retrieve the Valentines. Cut pieces of patterned wallpaper into strips, and cut out other attractive pictures, such as flowers or hearts, to use as decoration for the box. Attach the strips of wallpaper to the box in a striped pattern with Mod Podge or another sealer. Use the extra pictures to accent the stripes on the box. Allow the box to dry completely, and use large white letter stickers to label the box. Use Mod Podge to secure a piece of curled ribbon to a piece of floral wire. Add a hole to each side of the box and attach the wire through the holes to form a handle. Tape pieces of curled ribbon to the edges of the box and to the area around the handle's holes. Apply an additional coat of Mod Podge to the box, and allow it to dry.