have your treble up. if you have a wah pedal, have it midway then when you bend the squeal open the wah up completely (push it down) that will get you some means ass squeals. also if you dont have a wah or it is just in the way to run to the wah everytime, use sharper picks, and instead of one finger to do the squeal (on the fretboard, use two or 3 to bend it rapidly to make a wiggly squeal or slowly to make a progressive squeal.
Gain is your friend, but you can squeal on a clean channel so thats not completely true. just practice, youll have to find the sweet spot where you pick on each string at each fret place. Practice!!!