As Pam suggested, view Tom Silva's video. Squeeks No More, used in conjunction with your drill works wonders, even through carpeting, and you cannot see or feel the screws, as they are designed to break off, below carpet level.
You must measure carefully to determine best point of installation, but it's definitely worth the effort.
You can add more screws to the floor boards when they are loose. They usually sqeak because they are loose.
Sprinkle talcum powder between the floor boards to get rid of squeeks.