Creaking floor boards is not a serious problem but it can be an annoyance.
The main cause of floors that creak when you walk across them is the loosening of the floor boards. Over time the nails that secure the wood to the floor joists work their way loose. When weight is applied to the floor, the wood flooring rubs against itself or the nails and causes a squeak. Repairing the problem of a creaking floor requires resecuring the floor boards.
Walk across the floor and place a small piece of painter's tape every place the floor creaks.
Drill a pilot hole in the floor in the location of the pieces of tape using an electric drill with a 1/8-inch drill bit installed. Hold the drill at a 90 degree angle to the floor to ensure the holes are straight.
Insert a 2 1/2-inch wood screw into each pilot hole using an electric drill with a driver bit installed. Overdrive the screws so the heads of the screws are beneath the surface of the wood.
Cover the heads of the screws with a wood fill putty that matches the shade of the wood. Use a putty knife to smooth the putty into the holes over the screw heads. Let the putty dry according to the directions on the can.
Rub a piece of steel wool lightly over the filled areas to even out the wood fill and to blend it into the rest of the floor.