There is this, but it's not all that helpful in my opinion. It's more "How to post an answer" than "What makes an answer good?" I'm not sure if this is something we can change (cc @RobertCartaino), though. If not, making meta detailing what makes a high quality answer is a fantastic idea.
I don't really have time to write a detailed one, or I would, but I'd say any such post should cover:
- Detail: A one liner just saying "do this" is okay, but great answers explain WHY something works, any shortcomings the solution might have, and explain how to implement the solution.
- Pictures/Videos: Pictures and videos aren't required, but they can be really helpful when explaining an answer (i.e. if showing someone how to make some tool, then a video showing the steps is a HUGE plus)
- Link Excerpts: If you link off to a product or video include a short summary of the link if possible.
- Grammar/Formatting: Answers with good grammar and formatting are a lot easier to read and understand than giant walls of text with a bunch of spelling errors.
- Links to high quality answers: Examples of high quality answers are the best way to show folks what they look like.
There's probably some other things I'm forgetting about, but that should cover the basics. Just keep in mind that a resource like this doesn't mean you should just post a link to it on every page answer, with no explanation. The best way to help a user with low quality answers is to explain the major issue(s) with their answer, with advice on how to improve it, and then (maybe) link off to the guide (i.e. that product seems helpful! Could you update your answer to include a short explanation of what the product does, and how it solves the OPs problem?). Also, don't be afraid to edit an answer yourself and leave a comment explaining why you did so for the answerer. Sometimes the best way to teach is via demonstration.