Well, thumb pick hitting the head really is "stop doing that". The trick is to have it REALLY MATTER to you. If you avoid it with the same clear-headedness you avoid, say, walking in traffic against the light, it just won't happen. So the trick is to really notice it and convince yourself that it's "BAD".
As for the rasps you mentioned, that's similar, but it's not as simple as changing the path of the pick, as with thumb pick hitting the head. Using a little natural oil (gathered from the hair, or lacking hair as I do, the side of the nose or behind the ear) tends to lubricate the pick and help it wear to the point that there's less friction. It also has to do with the way the pick contacts the string, especially the crispness of that. A quick pick doesn't have much time to make noise, while a slower pick slides a bit along the string. My most effective way to get rid of pick noise (once I've got my nose oil in place!) is to just be aware when it happens, and "somehow" try to make it go away. My hand probably makes small, unconscious adjustments, with the desired results. Again, the trick is that you have to notice it and have it MATTER. That is key to correcting any bad habit.
Hope this helps!