You can give these series of lessons a try:

http://guitartricks.com/lesson.php?input=4137

It's a 9 page tutorial that goes through all the various types of harmonics including pinch, touch, natural, feedback etc..

The video is a little outdated and needs to be redone in Hi-Def but it should give you a clearer idea on how to accomplish this.

More specifically, these two lessons are aimed at pinch harmonics:

http://guitartricks.com/lesson.php?input=1618&s_id=35&c_id=10&ch_id=55
http://guitartricks.com/lesson.php?input=4227&s_id=35&c_id=10&ch_id=55