If you're
just papering the front of a soffit, simply hang the wallpaper over
the opening and trim the excess. Hold your knife at a 45-degree angle
pointing toward the ceiling to prevent fraying of the edge.
If you're
papering both the front and the bottom of a soffit, wrap the paper around
the front edge and install it on the bottom of the soffit and overlap
the wall by ½".
Next,
paper the wall below the soffit, attaching the paper to the overlap
with vinyl-to-vinyl adhesive.