Use a ladder to get close enough to measure the space above the stairs. If you want to minimize the time you spend on a ladder, estimate the area by measuring from the ceiling down to about the bottom of the wall while standing on the stairs.
Paint the area above the stairs an accent color. This draws attention to the area and makes it more of a focal point.
Hang one main focal piece on the wall that is large enough to draw attention without overwhelming the wall. Ideas include a large framed photo, artwork, decorative wreath or a large decorative panel made from fabric, wood or metal.
Hang smaller decorative objects around the main component of the space. Choose pieces that complement the design and color of your focal point to create a cohesive display. Ideas include smaller framed art, decorative tiles or artificial flower arrangements.
Install shelving in the space above the stairs if you want to display objects that you can't hang. Arrange the objects on the shelves to create the desired look.
Install recessed lighting or track lighting in the area so you are able to focus one of the lights on the display above the stairs.