Identify the squeaky stair tread or treads on your stairs. Hammer one finish nail at 45-degree angle that is pointed toward the front edge and one that is pointed toward the back edge of the stairway through the squeaky tread into the stringer on each end. Locate each nail approximately 2 to 3 inches in from the edges.
Center a nail set on each nail head and tap it with a hammer to set each nail approximately 1/16 inch below the surface of the wood.
Fill the nail holes with wood putty using the edge of a putty knife. Allow the wood putty to dry for 24 hours.
Sand the wood putty flush with the surface of the wood using a fine-grit sanding pad in the direction of the wood grain.
Touch up the filled nail holes with a matching wood finish using a small touch-up brush. Allow the finish to dry at least 24 hours before walking on the stairs.
Find the noisy stair treads and assess them from the under side of the stairs.
Slide a wood shim under each stair tread between the risers and stringers if there is a gap.
Tap the shim with a hammer until it is tight at each gap. Walk up and down the stairs. Add more shims as needed until the stairs are quiet.