a.. Prepare Floors - Make sure there are no nails or tacks sticking out of the floors if they are wood. Make sure the wood surface is smooth; if not, you might want to apply plywood over the floor. If the floor is cement, make sure the cracks are filled.
b.. Tackless Strip - A tackless script is a wooden batten with pins projecting up at an angle. You will want to apply these strips to base of the stairs, one right as the stair is going up; the other as the very back of the stair. This is how your carpet will be held down.
c.. Attach Padding - It is best to select a good padding, so you won't have any mildew under your carpet. Sponge rubber padding and urethane foam padding will not mildew. Urethane is just thicker than the sponge. Whichever you choose, attach it to the floor with a staple gun. Make sure it reaches between both tackless strips.
d.. Position Runner - take your runner of carpet and place it along the staircase. Start from the bottom and push the runner along the tackless strips. To make sure the carpet it tight, take a hammer and stair tool, and tap the carpet into the base of the stair. Repeat this at each stair before attaching the carpet to the next tackless strip. Repeat this to the top stair, then make a clean cut and attach the top to the carpet upstairs.
e.. Winding Staircase - if you have a winding staircase, you will do the same thing, but cut each runner to fit the step. You will need to use the hammer and stair tool to tap the excess carpet beneath the stair at the base. Repeat the same steps until you are at top step.