At least a few Stack Exchange sites have meta questions about what makes a good answer (and some suggestions that such a question should be included in the FAQ [now Help Center]). When a new poster provides a poor answer, it would be convenient to point the person to that resource.
(This short article seems inadequate and does not seem to be very discoverable.)
I think it would be useful to have general guidelines as a Help Center entry along with a site-specific resource. Some aspects apply to Stack Exchange generally, e.g., unsupported personal opinion is not useful. Some aspects would apply to the specific site or even to specific types of questions.
(This meta question on Mathematics SE suggested providing examples (presumably with explanatory text) of good and bad questions and answers.)