Given the large number of first time question askers who evidently do not really read the advice on how to ask a good question, I propose:
The site should require first time question askers to take a short quiz (e.g. five multiple-choice questions) on how to ask a good question, before posting their first question. If they pass the quiz (e.g. at least 80%), they can post their question; if they don't pass, they can try again after some period of time (e.g. one hour).
This may increase the quality of first questions.
Such a quiz would discourage some people from starting to ask questions. Most of those people would be people who are not willing to familiarize themselves with the site expectations.
Examples of quiz questions:
Your question can be ______.
A. an open-ended question that could lead to discussion/debate
B. a specific question that has a definite answer
C. all of the above
Before you ask a question, you should ______.
A. ask your teacher your question, if you are a student
B. check a math-specific search engine (such as approachzero) to see if your question has been asked online before
C. all of the above
Your question should appear in ______.
A. the title of your question, if possible
B. the body of your question
C. all of the above
Which of the following are acceptable ways to present mathematical working in your question?
A. mathjax
B. photos/screenshots of handwriting
C. all of the above
Which of the following is a required part of your question?
A. the context of the question
B. a description of what you have tried so far, and where you are getting stuck
C. all of the above
Within each question, the order of some of the answer choices could be randomized, so that if people try to look up the answers online, they will at least have to read the words to work out the correct answer choice.
EDIT:
Today, more than one year after I made this proposal, I feel even more strongly than before, that it is worthy of consideration. None of the comments convinced me otherwise.
There are too many posts from new users who are unfamiliar with the site expectations (typical example from today). Whatever mechanism is in place to prevent this, is not working.
Maybe test my proposal with a small sample or something? Who knows, it may actually be effective.
(As of now, my proposal has $10$ upvotes and $9$ downvotes.)