Clean out the debris in the veneer of a stair riser with a toothpick. Wipe the crack with a tack cloth.
Squeeze a tiny amount of yellow wood glue into the crack until the crack is filled. Press down on the veneer on either side of the crack, and wipe away the excess glue with a rag.
Wait until the glue is completely dry. Sand off any excess dried glue with a fine-grit sandpaper. Wipe the crack with a tack cloth. Paint or varnish the riser to match the staircase.
Remove riser veneers that have cracked all the way through by pulling up the veneer nails with a claw hammer. Sand off the old veneer glue with fine-grit sandpaper. Wipe the riser with a tack cloth.
Apply yellow wood glue to the back of a new piece of veneer. Glue the veneer into place on the riser. Nail small veneer nails on the left and right sides of the veneer to hold it in place on the riser.
Locate loose risers by listening for squeaks when walking up and down the staircase.
Hammer a shim into place between the loose riser and the stair tread on the back of the staircase if you have access to it. Trim off the excess length of the shim with a hand saw.
Hammer a shim into place between the loose riser and the stair tread on the front of the staircase, if you cannot access the back of the staircase. Trim off the excess length of the shim with a hand saw.
Drill a hole into the riser and tread at a 45 degree angle, if a shim does not fit between the riser and tread.
Drive a nail from the top of the riser into the bottom of the tread to fasten the riser and tread together and prevent squeaks.
Remove scuff marks on a riser by applying scuff mark eraser with a rag according to the manufacturer's instructions. Let the riser dry completely.
Repaint the risers with a high-gloss latex paint that resists scuffing, if you cannot remove the scuffs already present on the risers using the eraser.
Vacuum or sweep your stairs on a regular basis to remove grit that can contribute to the scuffing of the staircase risers.