Ask Question dialog has an appropriate faint overlay text in the Title input area:
what's your math question? be specific.
(Aside: this seems to suggest to new users that proper capitalization on Math.SE is optional.)
Capitalization aside, the text serves its purpose by telling users that a question must have a descriptive title. It is easy to tune out any links in sidebars, but it is impossible not to notice the text overlaying the input area in which you are to type. Of course, this overlay disappears as soon as a user begins typing in the field.
I propose to add a similar overlay text in the question input area, as on the mock-up below. One possibility is the famous quote by Arturo Magidin. I think it applies to questions at all levels.
It is helpful if you say in what context you encountered the problem, and what your thoughts on it are.
The current dialog does say
Provide details. Share your research, but this is done in the sidebar (easy to overlook), and in somewhat cryptic language ("I should share my research? I'm not doing math research.") The advice by Arturo Magidin is frequently quoted in comments, and in many instances users respond to it by improving their questions. The site would work smoother if it was taken into account prior to posting.