Since I'm still a newbie with GTD I am a little hesitant adding my approach here, but here it is:
I process my NAs randomly (next index card picked with closed eyes) - I understand that this is not always practicable (taking lesson 3 of your fingerpainting class in your office...) and not the most effective way to go, but it helps me argueing with myself and sometimes its great fun. Whenever I feel myself resisting too much (does not happen often) I leave it out. When I'm done I extract a 2 minute (let it be 10) action for some less ambitious outcome and do it right then (so I don't have a bad feeling for not doing sth.) and break down the rest for the next iteration.
This is no way to go in the long run, but it really helps me getting a feeling for the maximum size of some atomic next action.