1997 Ford Explorer 97 explorer break squeal

I recently inherited a 97 explorer and I had a quick question about the brake pads. When braking, there is a very loud squeal unless I brake hard enough. I looked at all the pads without taking the wheels off, and each look like they are brand new. They all have at least 3/8" left. I do believe atleast one rotor is warped though, as is apparent through the pedal. I'm assuming that the pads are glazed and I was going to sand them down with some 220 grit and break them in again. Does anybody have any good break in tips? Also should I sand the rotors? Thanks guys.