And, really, that carpet was great for catching the dust and debris that I dragged out of the basement every time I walked upstairs during the renovation, so I left it on until the bitter end. By the time I was ready to remove the carpet, I had plenty of inspiration pinned on Pinterest to help me decide what to do, but the one below was definitely my favorite.
At just under five feet long, one Söften rug wasn't long enough to cover all the stairs, and so I bought three of them, hoping that the three would be enough to cover my whole staircase (true to form, I didn't actually measure the staircase before buying or installing the runners). The bummer was that when I got the rugs home, they were about half an inch too wide for my staircase (did I just mention something about how I didn't measure?). Undaunted, I trimmed off the hems on the short sides and pressed the long sides under and sewed new hems along the edges.
Using two Ikea Stopp anti-slip rug underlays (a total bargain at $3.99/each and just the right width) and my pneumatic staple gun, I made my way down the stairs stapling the rug to the top of the riser, the intersection between the riser and the tread, and then under the tread nose.
If you are contemplating installing a similar runner, I would definitely recommend using a pneumatic stapler (as in, a stapler that is attached to an air compressor). My electric stapler would not have been able to do this project. If you don't have an air compressor and pneumatic stapler, you need to beg, borrow, or steal one before you attempt this.
When I got to spots where I needed to join the end of one rug with the beginning of another, I simply turned under the end of the new rug and stapled it up under the nose of the most recently covered tread, right over the rug that was ending. Very simple and not fussy at all. Somehow I managed to have each rug end right in the middle of a riser, not a tread, so I didn't even have to cut them down...except the last one. I ended up with about 18" of rug left at the end. I assume this is due to my very careful planning and measuring.
One place I made a mistake was in keeping the rug centered on the staircase. It would help to use painter's tape to mark the edges of where the rug should go before you start stapling. Or at least step back and take a look every once in a while. But, since it isn't horribly lopsided, I'm not worried about it.
Frankly, the cat uses this staircase more than anyone else in this family (to get to her litter box in the utility room) and I don't think she cares if the runner is perfectly straight. Or maybe she does? She is a cat, after all.
And, lastly, the louvered door in that photo above? Yeah, I added that sometime between the "before" and the "after," too. You can see my pocket door tutorial here.