How would you fix a squeaky floor?

Generally, you would have to identiify where the squeaks are coming from, lift the carpet in those areas and nail down the floorboards more securely by adding extra nails. At least, that’s the way I know how to do it.

Yes, you will have to pull up the carpet.
Sawdust in the cracks works wonders.

have you tried selective hearing…...?

I suppose you might be able to nail down the floorboards without pulling up the carpet, but it would be harder… and you’d have nails in your carpet.

Are you saying the entire house is squeaky? A while ago a friend of mine had 1 squeaky spot which was exactly at the entrance of the room. Turns out the floorboards were a little too long. Just looking at them everything was fine, but if you put your weight on one of the floorboards they bend a little and expand in each direction. As there was no room to expand, every time you set foot on of the floorboards you hear wood pushing against wood, and thus creating a squeaky sound. So how did he fix it? By giving the wood a little more room to settle in when under pressure. He just sawed off half a centimeter of every squeaky floorboard.

Edit: My answer is not really a direct solution, just something to look into and one of the many possibilities of what could create the squeaky sound.

WD-40?

Find your squeak. In the corner closest to the squeak you may need to pry baseboard and shoe mold off the wall if its on top of your carpet. Now you can pull the carpet loose from the tack strip. The carpet pad is probably stapled down so carefully pull it up so you don’t tear it up. Your squeak will be over a joist and probably at a seam of your subfloor. Use long screws not nails to fasten your squeaky area back down. Nails tend to pull back out a lot easier than screws. Slap staple your carpet pad back down. Roll your carpet back out and try to get any slack out then kind of work it and step on it so it sticks back to the tack strip. Put your baseboard and shoe mold back on and your done.