I would first start by nailing off the subfloor. Try and locate your squeaky areas. There probably at a seam. If you can get at them from below, add some blocking spanning between the joists. Use construction adhesive and screw the blocking between the joist and from above. If area is not accessable, you can make the repair from above. Cut out the area from above and then add the blocking and glue and screw the subfloor back down. After the subfloor is repaired lay down a 1/2" cement board with thinset and fasten. I prefer screws as opposed to nails. Good luck..