Specificity of questions is already encouraged in the site documentation.
But with MO suffering a plague of "what is your favorite ..." queries, there is a point that apparently needs more detailed negative instructions, and especially for the question titles:
To the extent possible, adjectives used in questions, and especially question titles should have objective or mathematical interpretations. e.g., "Large", "optimal", and "unique", are much better than "nice", "best", and "special".
It may be useful to have a short slogan expressing this advice, such as "AVOID PSEUDO-DESCRIPTORS!".
Also, as a practical matter and advice for editors: deleting all these pseudo-adjectives seems to improve the question titles in every case. It's hard to come up with an example where words like "favorite", "good", etc improve the question.