Pinch Harmonics

Ok pretty much you strike the string with your pick and your thumb at the same time. I put the edge of my thumb on the edge of my pick so the string is played by my pick and then my thumb, but almost at the same time. I always use some vibrato as it squeals too. I'm not that good at explaining it, someone else could better I'm sure. Failing that look around on the net, there's plenty of sites that teach guitar techniques and stuff.
 
Like most things musical, practice practice practice. Vehemens described the technique pretty well, but I'd like to add that what you want to do is immediately after the pick strikes the string, you want the edge of your thumb to lightly touch the string to hit the harmonic. Move your picking hand to different positions, there are harmonics all over the place (some stronger than others). Lots of distortion helps them ring out, and again, practice practice practice.

On bass I strike harmonics with the pinky side of my palm, when slapping anyhow. I slap then quickly rebound my palm to strike it, I'm sure I didn't make that technique up but I've never seen anyone else use it. :)
 
ok yeah that's pretty much it. However, if you still can-t get that to work, try using the edge of your little finger instead of your thumb. That's what I use all the time and I find it give a better harmonic. Try doing a touch harmonic (play a note and then lightly touch the string e.g. 12 fret spaces above the fretted note) and use that principle in one go for ther pinch,.
 
Yeah, it's just practising the technique and seeing which way to play it suits you best. When I first learned from a mate of mine he said he learned them by striking the pick upwards and using his index finger to sound the harmonic. Either way these guys have mentioned will work.
 
If what the doods mentioned up their didn't help entirely hears my description. First, Remember the more gain, the easier it is to hear them. Second, you'll get a better sound out of your bridge pickup. I found the easiest string/note to learn it it on is on the 7th or 9th fret of the G string. And finally, hold the pick more perpendicular to the string like your gonna take a chunk outa it when you pick. The important thing to do when you pick the string is to make it snap back and just lightly hit the middle of your thumb (the part of the thumb that is just before where you're holding the pick) Also NOTE. Their are different hot spots on the string aswell, so pic at different spots up and down on the string between the bridge and you neck pickup and you'll find several differnt squeals, while some spots won't give that good of squeals. I hope this helped.
 
Yes, practice is the most important part of learning pinch harmonics. You can learn the basic form, but the skills come with time. Eventually you'll be able to pretty much hit one whenever you want to and it will be second nature, even get some squealing on the low strings.