Fix the baluster or stair tread
First of all tighten the stair tread or baluster. All you have to do is, drill a pilot hole at an angle and then insert a large nail or screw into it, using a nail set.
Secure a newel post
Use a drill machine to bore a home counterbore hole right at the base of the newel post. Now, bore/drill a pilot hole through the counterbore hole and into the framing right behind the newel post. Place a medium washer on a large lag screw and gently place it into the hole. Carefully drive in the screw, using a socket and ratchet wrench. Use a sandpaper to smooth the surface of the newel post.
Fix a loose banister
Bore a counterbore hole into the wooden mounting plate, suing an electrical drill machine. Drill another hole to insert the screw-shank nails through the wooden mounting plate. Now use a wood screw to tie up the plate to the wall along the staircase.
Sand worn stair treads and handrails
Use a sponge sander, profile sander or sandpaper to smooth the surface of the handrails, removing threads. Remove the wooden particles with tack rag and vacuum the area around the staircase.