Locate the joists under the floor with a stud finder. Mark their locations with masking tape.
Place a heavy weight of at least 200 pounds onto the squeaky floorboard to hold it down.
Drill a 1/16-inch pilot hole diagonally through the floorboard and into the joist beneath it.
Drive a spiral flooring nail through the pilot hole, securing the floorboard to the joist. Use a nail set to sink the nail head slightly below the wood surface.
Remove the weight and test the floorboard to see if it still squeaks. If it does, reapply the weight and add additional spiral flooring nails until the squeak is eliminated.
Fill the countersunk nail holes with wood putty that matches the color of the floorboard. Allow the putty to dry and then lightly sand it with 180-grit sandpaper.