How do you stop the floor from squeaking?
The main cause of wood floors squeaking is wood shrinkage around the nails. If you can localize the areas that are the worst, a common way to minimize squeaks is to drive screws up from the bottom through the subfloor into the hardwood. Be absolutely sure to use screws that are long enough to grab the hardwood, but short enough not to stick through.

If you do not have hardwood floors then you'll have to decide among a few different techniques appropriate for specific floor coverings, ie. carpet, tile, vinyl etc. 

With carpet, for instance, there are special breakaway screws (such as these made by McFeely's) that can be installed from above. With tile or vinyl, the screw from under method is often the way to go.