To get a good squeal put the pick-up selector on the bridge pick-up, have the treble up and a good amount of gain. I hold the pick so that only about 1-2mm is sticking out, at a right angle, from my thumb. This also makes tremelo and alternate picking a lot easier. Besides that, just practice a lot. It's like a lot of things that once you get the hang of it, it's simple.

Also, I had a bit of trouble when I started to do pinch harmonics because I tried Zakk Wylde's way of using the fingernail on the picking hand's forefinger, instead of the thumb. Once I tried using the thumb, it was really easy.