If it's the pad squealing, do not spray any kind of lubricant on it. Sure, it will stop squealing but it will also stop stopping you.

Toe-in is usually the problem as Corsair said. The pads may also be glazed. Open up the brakes and use an emery board on them. You can probably find instructions on how to adjust the angle ion Sheldon Brown's web site or just a general 'net search. Just a very thin piece of cardboard under the back end of the brake while you adjust the angle.