Verbal Judo is by far the best practical guidance on this kind of thing that I've seen.
There was actually a different talk that introduced me to it, where the same speaker was talking to an audience of cops, which I liked a little better. In that one he talked more specifically about the standard language of policing (often, giving people an order, and if they say no you just say it again louder or get physical with them) and how it's not the best way he found to be effective. He told a little story about a guy he arrested on a felony warrant (peacefully, after a while) who said he was the only cop who'd ever talked to him with respect. But, this video seems pretty on-target to what I liked about that original one (which I can't find right now for some reason).