Neil Young hammer-on style strumming

Hey,

I would really like incorporating some pull offs and hammer on's into my strumming style. I love the way Neil Young does it in a lot of his songs, most notably for me are the songs "tell me why" and "needle and the damage done". Question I have is how do you know which notes to hammer onto, or which progression sounds good.

David Hodge has an excellent article about it called "Tricks of the Trade," but I'm having trouble coming across any other articles that teach this sort of thing. Any advice on this technique will really be appreciated, thanks!