Stack Overflow's rules have grown very complex and often counter-intuitive over the years. That doesn't mean they don't exist for a reason, but grokking SO's culture can be really tough even for good-faith newcomers.
Many people learn much, much better from real-world examples than from a huge list of abstract rules.
I know - I'm one of them.
To better guide these people, we should show a curated and annotated list of good and bad example questions. This list should be extremely easy to reach - it could for example be a 2nd tab on the "How to ask" page. It should be a separate page, maybe with questions listed in 2 columns.
Each example is a full question, with an explanatory "what's wrong with this question?" paragraph underneath. The paragraph will be very curt and to the point.
What's wrong with this question?
It's a "shopping question" asking for a product recommendation. Questions like this are off topic on Stack Overflow: they frequently lead to low-quality content and subjective opinions.
Thinking of the extreme problem cases is easy. Too vague, Gorilla vs. Shark / Shopping question, Duplicate / too basic, Multiple questions in one, Wall of code... But we should also cover the more subtle cases where a question looks perfectly intelligent, but is not a good fit for the site.
Thinking of good examples is less easy - I can think of
- Great title
- Question body giving a lot of detail, but not too much
- Good structure (introduction / question)
^--- this obviously needs more thought.
The list could be curated by the community, or staff, whatever works.
Ideally, there would be example questions on a per-tag basis, at least for the big tags.
A "before" / "after" view might also work: How do I fix a problematic question?
The examples should be linkable so they can be used in communicating with authors of problematic questions. I can't see a way to misuse this in a rude way as there was with "What Stack Overflow is not".
Also, I think this would be a great help for dealing with the language barrier. An example is going to be way easier to grasp than a thousand words if you have trouble parsing the language in the first place.