Sticking points for me were:
- You need a good amount of overdrive or distortion. The harmonic is a weaker / quieter sound, and the compression / expansion you get from overdrive / distortion helps bring the sound on par with the non-harmonic notes.
- Others said this already, but yes, location matters. And the harmonic locations change depending on which fret is engaged. There is more than one location for each fretted or open note, each with different pitches /sounds.
- Pick grip. You can't have too much of the pick exposed from your grip, because the harmonic is created by your skin touching the string the instant after the pick strikes it. If the pick sticks out too far, your skin will never touch the string.
I discovered pinch harmonics by accident when I was in a college band back in the late 90's. I would strike a string hard by coming down on it from well above the guitar body, and sometimes would get a harmonic tone instead of the fundamental. I think what happened was that my thumb "got in the way" because the harder strike of the string made it take a big swing that brought it into contact with my thumb just before my hand cleared the string location.
These days, whether it's right or wrong, I have 2 different ways I approach these. One is to "scoop" the string when I strike it. I usually play with somewhat of a downward pick slant, which has the tendency to make the skin on my thumb clear the strings and not touch them. So by "scoop", I mean that I make a small rotational movement when I strike the string to change from a downward slant to an upward slant which then brings the skin on the side of my thumb into contact with the string after striking it, and sounding the harmonic.
If I want to hit a lot of pinch harmonics in a row, the other approach is to rotate my wrist a bit so that I have an upward pick slant and can more easily bring the side of my thumb into contact with the strings as I strike them.
I was bad at pinch harmonics for a really, really, really long time. Like, 30 years. Only started getting better at them within the last few years. So don't feel bad, there are others of us that also find them more difficult than other aspects of the instrument. But once you decide to start learning them and practicing them, setting a goal has a tendency to make you practice with a purpose and get better.
