Here is a true story about a less-than-gifted dog of the Labrador variety that lived in a two-story town home. The unfortunate canine would often venture up to the second floor to see if her children, who were at school, had secretly returned. The rest of the day she would spend at the top of the stairs, whimpering, because her padded feet tended to slide on the polished wood surface of the stairs, and this frightened her. Each day she would remain stuck at the top of the stairs until her owner returned and reminded her that she'd successfully navigated the stairs thousands of times, or until her children returned and her excitement overwhelmed her fear. Eventually, the dog's owner resolved the issue by installing a carpet runner on the stairs, which gave the dog better traction.
But carpet runners don't just offer comfort to neurotic dogs, they also offer better grip for those in dress shoes or stockinged feet and a softer landing for those who do slip. They're also often a good deal prettier than unadorned stairs and not too difficult to install.
For the most part, the tools you need to install a carpet runner--utility knife, framing square, tape measure, and rubber mallet--are likely already in your tool box. But you also need a few specialized tools--a knee kicker, an electric stapler capable of firing 9/16 inch narrow-crown staples (you can get this from a tool rental store), and a carpet tool, which you can get for under $15 at a home improvement store. You also need tackless strips and a carpet pad.
For clarity's sake, here are a few definitions:
To ensure the carpet runner is centered, begin by subtracting the width of the runner from the width of the staircase and divide by two. Using a pencil, lightly mark each stair that distance from each edge. This is where the edges of the runner will sit.
For each stair, cut a length of tacking strip that is two inches less than the width of the runner, and a piece of carpet pad that is the same width as the tacking strip, and three inches longer than the depth of the tread. Place a scrap piece of tacking strip on top of the first tread and press it against the riser. Using the scrap piece as a spacer, press your first tacking strip against it, centered between your pencil marks, and nail it into place. Repeat for each stair.
Next, install your first piece of carpet pad. Begin by stapling the front edge of the pad flush against the front edge of the tacking strip. Pull the pad tight, and staple it to the bottom of the nosing. Staples should be three inches apart. Cut off excess pad. Repeat for all stairs.
Check the bottom edge of the runner to make sure it's square. If not, use a carpet knife to square it. Staple the bottom edge of the runner to the bottom of the first (lowest) riser. Staple every three inches, and make sure you push the staple gun through the pile of the carpet so that the staples are hidden.
Next, tighten the runner over the first tread, keeping it centered. Place the kicker in the center of the tread, two inches from the riser, then hit it with your knee. This tightens the carpet and attaches it to the tacking strip. Repeat three inches to the left of center, then three inches to the right, and so on until you reach the edges. If it doesn't look right, pull the carpet up and start the step over.
Use the carpet tool and rubber mallet to push the carpet into the crease between the tacking and the riser. Staple the runner to the tread at each edge of the tacking, and at each edge two inches up from the bottom of the next riser. Repeat these steps (kicker, carpet tool, staples) until you reach the last riser. At the top, cut the runner so that it butts against the bottom of the nosing, and attach it to the top of the riser, stapling every three inches.
Sources
http://www.thisoldhouse.com/toh/how-to/intro/0,,392360,00.html