Simple hardwood floor fixes:
1. Silence a squeaky board. After locating the offending floor board press down on it and drill a 1/16 inch pilot hole into the board at an angle until you reach the sub floor (a little over 3/4″ on most floors). To avoid splitting the wood make sure you are at least 3 inches form either end and in the center of the board. Next drive a 6d finish nail and set with the appropriate nail set. Fill the divot with color matched wood putty.
2. Scratches, you can cover up scratches in your hardwood floors as the happen by using a color matched stain stick (stain filled marker) available at most hardware stores.
3. Remove stains. Moisture can cause a discoloration of the wood floor to remove this first sand off the finish in the offending area then scrub with a solution of hot water and oxalic acid powder (wood bleach). Rinse three times with plain water. It make take several applications to remove a stubborn stain however once the stain is gone wait until the floor is fully dry and refinish the area. (You can speed up the drying time with a fan)
4.Spot refinish. Tape around the trouble area and then sand with 80 grit sand paper. Next sand the area with 120 grit and then apply two coats of polyurethane. Make sure to allow the proper drying time per coat.
5. Fill gaps. You can fill gaps in wide board flooring using manila rope or no-tar oakum (a jute based fiber used by plumbing contractors).