its quite easy to work out where the sweet spots are. at least roughly. u basically divide the distance between the fret u are pressin down to the bridge by a whole number. as the number goes up the pinch harmonic will be higher. but also harder to make it sound. iin general but it will depend on your pickup position and choice. the reasons for this are harder to explain and u dont rly need to know to be able to play them.

doin pinch harmonics is not an easy thing, although like anything once u got them down they are fairly easy. try and leave as little of the pick showing when u do them. hit the string with the pick and then fractionally later with the a bit of ur thumb. ur thumb should only just glace of the string. it takes practice. and if u want a better explanation of how to do it ask. hope this helps