As far as I'm aware Artificial Harmonics and Pinch Harmonics are different animals.
Artificial/Tap Harmonics: Think to that part of the Lamentations DVD when Mike is tracking that solo in Wreath. That part at the end which him and Peter kept fucking up and laughing about. That was an artificial harmonic. When you essentially tap a section of the string that naturally produces a harmonic.
Pinch harmonics: Are when you essentially pick a string but then briefly brush it with your thumb straight after (some people even do it with their forefinger... I don't know how the fuck, but they do). What happens is a similar thing to the artificial harmonics. Your thumb, briefly brushing over the string after it's been set to vibrate by the pick triggers the harmonic that corresponds to that section of the string, and as such you get a very pronounced harmonic sound that you can vibrato, whammy dive, whatever the living hell out of.
If I'm wrong about my definitions, please feel free to correct me. It's been a while since I've looked up the terminology... I just learned the techniques and that was it.
In regards to tips. The only one I can give is to practice. It took me weeks to be able to even get the sound happening on an off-chance. Over time I've built it up to be able to play one at command, and progressively faster over the years too. All you can really do is keep trying. Just keep pinching that damn string.