Locate the exact squeaky spot by walking on the floor
Mark the squeaky area with tape or chalk
Tighten loose floorboards or subfloor screws
Drive screws through the floor into the joist below
Use finishing nails if screws are not suitable
Add construction adhesive between the subfloor and joist if accessible
Sprinkle powdered graphite or talcum powder into small gaps between boards
Shim gaps between the subfloor and joist from below
Install a squeak-repair bracket or kit from below
Replace damaged or warped boards
Secure loose carpet tack strips if the squeak is under carpet
Check for loose nails and replace them with screws
Test the floor after each repair
Call a professional if the squeak persists or the structure is damaged