That's a difficult question.  I think a lot of it is a matter of just doing it on a day-to-day basis in every discussion we have on WP, whether on an article talk page, a deletion discussion, or at VP.  Maybe there could be a guideline (or even just an essay) urging people not to rely on rote policy citation regurgitation in lieu of substantive explanation (maybe there already is one somewhere?).  And reminding people that citing policy is at best only half the work: you may have settled on what you think governs the issue, but you still need to convince others of the best way to apply it in a particular circumstance.  To do it properly the focus should always be on what the best editorial decision is, not just the superficial level of what complies with codified policy or guidelines.  Yeah, all that should be written down somewhere if it isn't already.  In another guideline for people to cite.  ; )

I think also we could go policy by policy, guideline by guideline, and ask ourselves whether its purpose is clear.  What does it substantively accomplish.  That may not always be evident; it may reflect the way consensus tends to go without an articulate reason as to why.  A history of how the policy was written could be interesting, but maybe not that helpful, and it would be difficult to summarize.  Just looking at the edit history of a particular policy or guideline may omit a lot of developmental discussions that occurred on the talk pages of other policies, the Village pump, or even user talk pages.  '''' (talk'')