You could attempt to contribute to the community by writing a "guide" with some pointers for this (I'm not aware that there is one).
Would it be of any use, really? After all, anyone that could possibly want anything to do with it should know what actual spam is. I don't think that individuals which would like to increase their post quality would be questioning whether their posts are spam or not.
Most people should be able to understand that if their posts are all one-liners or vague and generalized recycled garbage, or agreeing posts, then they are spam. If the post isn't adding anything, then it's spam. What's so hard to understand about that?
However, I think it's good to question whether your posts are useful or not. IIRC, there have been a few times that I've written down a lengthy post to realize that I'm on the wrong page... and then deleting it.