How can I stop a kitchen floor from squeaking? We have the carpet up, so can work on the subfloor.

Renail the floor using ring nails. Make sure you get the nails in the joists. Use lots as they are cheap. Watch for old loose nails and remove them or pound them down.

Or screw it off into the floor joists

Its not enough to just nail or screw the floor you've got to find the joists and with the carpet up it will be easy to do it.