First lay a Seriously Good Dust Sheet along the area you will be painting and use some Seriously Good UV Tape to secure it in place. Top tip, tape the dust sheet to the carpet by first adding the tape to the edge of the dust sheet, with a small (about 1 cm) upturned lip resting on the skirting board or edge of the stairs. Now use your fingers to pull the carpet back slightly and push the tape down. Do this as a single motion then release the carpet. It should spring back into place and you will have a nice seal protecting the carpet.