To restore an old wood floor, sand it well to remove dirt, paint, stain and sealer. Apply the fresh stain and, once it is dry, apply sealer. Before adding a second coat of sealer, allow the first one to dry completely, then sand the floor with a pole sander.
For older wood floors, a drum sander is more effective than a square sander in cleaning the floor down to bare wood. The drum sander cannot reach all the way to the wall, so an edger is necessary to sand those areas. If the floor has old water damage that does not come off with sanding, the staining process may be able to hide it. If not, replace the damaged area with new planks of wood. After staining and allowing the floor to dry, sweep to remove dust or other particles prior to applying the sealer.