Have you seen Pinball 101? I can't remember if it really gives a "tip" for that move, but it has a lot of info for the $3 or so that it goes for on the iPhone. Great menu to view all of the useful stuff and skip the rather annoying segues.
Other than that.. practice, practice, practice. Play some games and just make it your focus and try it whenever possible. I find the slot machine shot kinda tough because it rolls down pretty slow..