Hmm, what to say other than just keep practicing. I remember some 6 years ago when i first started and i couldt do it either, and now, its like i dont even have to try and i get a perfect hammeron-pulloff every time. (unless of course its a series of hammer ons, then it is a bit tougher.

tips. practice with your middle finger then work your way down to your ring finger then pinky. Pluck the string with a note fretted with first finger, then hammer on with middle finger until you get it to sound right. Then as i said move down to other fingers, and move to other strings as well.. later

chris