A: The approach is different for each. For carpeted floors #8 finish nails work well. Find the floor joist by pounding on the floor listening where the less hollow sound occurs. If you are lucky and the squeak is in a room that boarders one of the outside walls of the narrow side of the house, you can measure in 9 inches from the inside wall and then in 16 inch intervals until you get the area of the squeak, should put you on a joist. keep in mind the joist are only 1 1/2 inch wide and run parallel to the shorter side of the house(usually front to back). Sink the nails slightly below the surface with a nail set to avoid detection. it is usually necessary to nail on two or three joists and 6 inch apart along the joist and for 1 or 2 feet.
For linoleum and also an alternative to the above for carpet, you will need access to the subfloor from the ceiling in the lower floor. Using wooden or small metal wedges drive them between the joist and the subfloor. be careful not to separate the two but just insert a small amount of the wedge into the space being careful not to lift the floor up. We also carry a kit for carpet floors. it is ace number 5106125 and you can see it on www.acehardware.com.
-Bill the "Helpful Hardware Man"