Remove all books and other items from the IKEA Billy bookcase and set them aside.
Clean the bookcase with some detergent and water. Then wipe the bookcase dry with a towel.
Smooth matching wood filler into any cracks or chips in the bookcase. Wipe away excess with a clean cloth.
Sand down the dried wood filler and any other uneven surfaces on the bookcase with medium-grain sandpaper.
Paint or stain the bookcase shelves and interior and exterior sides, but not the back of the case. If you elect to paint, first apply primer to the unit with a paintbrush. Allow the primer to dry thoroughly. Then apply one to two coats of paint to the unit. Allow each coat to dry before applying a second coat. If you are staining, wipe stain on the bookcase with a dry cloth. Allow the first coat to dry, then apply a second coat of stain.
Once they are dry, slide the shelves out of the Billy bookcase to gain access to the back of the case.
Smooth contact paper over the back of the case, or paint it a different color to make it stand out. To install contact paper, measure the width and length of the space. Cut the contact paper to size. Remove the plastic backing, and smooth the paper to the back of the bookcase.