The wall under your stairs may seem as though it's wasted space, especially if it doesn't have built-in storage, such as a closet or shelves. You can use the walls under the stairs to make a decorative statement, though, especially if the stairs are in an area of your home that sees a lot of traffic. If you'd prefer, hang shelves on the wall to add decorative touches such as a vase of flowers or knick-knacks.
Use the level and pencil to draw a straight line up and down the wall that's the width of a strip of wallpaper.
Remove the backing from the pre-pasted wallpaper and dip it into a tray filled with cool water, as directed on the paper, until the wallpaper is wet. Let the wet wallpaper rest for 5 minutes before hanging.
Smooth the strip of wallpaper until the wall, using the sponge to apply and the smoother to push out any air bubbles. Lay the next strip of wallpaper right next to the first. Do not overlap the edges of the paper. You want each strip to rest next to, not on top of, the other.
Use the craft knife to trim away excess paper on the sides and bottom edge of the wall and along the top, slanted, edge of the wall.
Paint the wall under the stairs using a deep, bold colour instead of wallpaper if you prefer. Choose a colour that coordinates with the main colour on the walls of the room. For example, if the walls are light blue, use a deep blue or a deep yellow on the wall under the stairs.
Hang several wall shelves on the wall and set decorative objects, such as a vase, on them. For the most impact, use a single shelf in the centre of the wall under the stairs.
Hang an assortment of picture frames on the wall. Lay out the frames on the floor before hanging so that you can play around with the design and pattern of the frames, then transfer the frames to the wall.