Mandatory guidelines can be counterproductive if they are strictly enforced. The list of stipulations that ought to be adopted as mandatory should be very, very short. Perhaps as short as answers need to address the question at hand and clearly articulate a position.
There are a lot of suggestions here and sure to follow that are prima facie guidelines that will improve the majority of answers. But there will always be some unanticipated situations that would benefit from the latitude to present a solution in an unorthodox manner.
To that end, I suggest that the majority of guidelines adopted should be in the form best practice guidelines, strongly worded advice.. but still short of absolutely mandatory. Such guidelines can still be enforced by moderators and highly ranked users who can bridge the remaining gap while still having some discretion to allow well thought out, creative, unanticipated and valuable answers that would occasionally run afoul of rigid guidelines.