Sometimes on my own questions and other people's questions, I see users posting very useless comments that just show they only read the title of the question, and blazed through the specifics explained below. I have even seen answers that are like this, and it is extremely annoying, because they basically restate the OP's assumptions as their answer, then the OP has to refer them to the full text of the question and ask the question again. I understand that part of the rules are to read the question fully and understand it before you can answer, but how can we encourage users to actually do this?
This is a technical writing problem, and it is your problem as the author.
Start with a good, representative title. If your title reads like a different or simpler question than you intend then you have communicated something other than what you intended.
If you can't state the question in the title there is a good chance you are trying to cram too much into a single question. Remember the model is one-question-multiple-answers, not several-questions-many-answers.
Make sure the question is suitable for the site. Many beginners want to hear opinions on the ontology of various branches of physics and think a question of this sort would automatically be good for the site without realizing that regulars have seen them many, many times and often consider them to be unproductive philosophy suitable mostly for post-tenure noodling.
Use the right vocabulary. If the problem has a usual name or formulation, use it. This implies that you need to have done a bit research, but that is OK, because if your question is really simple you may find the answer on your own before you post.
More broadly, choosing your words carefully is a part of good technical writing. The ideas we want to express are often pretty complicated and it does not help to introduce extra ambiguity by using an not-quite-right word. Similarly, awkward and unnecessarily-long sentences add to the reader's mental burden.
Be aware that the formulation used in pop-sci treatments is often different from that used by professionals in important ways. Professional quantum physicists rarely perform "the double slit experiment" as such but often perform "diffractive scattering" experiments (a more general category that works on the same physical principles).
Consider including an abstract paragraph. Tell them what you're going to ask them as early as possible.
Don't bog the reader down with a lot of detail without letting them know where the effort of reading and understanding all that stuff is going to take them
Make good use of the formatting tools available. Note in particular that "good" does not mean "copious". If everything is emphasized, then nothing is emphasized.
Don't overlook that the tools on Stack Exchange sites include headings, lists, horizontal rules, and images in addition to changing the typeface.
Finally, I"ll note that good technical writing is not easy and is a learned skill. The effort you put into doing a good job writing posts and comments on technical Stack Exchange sites will be rewarded not only here, but on the job if you are in (or go into) a technical field of work (because communication is a big part of every job in all such fields).
I agree with knzhou that it is more profitable to discuss concrete (linked) examples. As scientists we like to see the evidence and judge for ourselves rather than adopt somebody else's opinion on an issue.
Your question seems to imply that the fault is with those who post comments or answers. Whether or not that is true, I agree with dmckee that if question-setters want better answers, it is their responsibility to ask better questions.
DanielSank reminds us that detailed advice about how to ask (and how to answer) already exists. I think the reasons it is overlooked or ignored are that (i) it is not prominent, so users don't know it exists or where to find it, and (ii) it is far too long.
This leads me to suggest that question-setters be advised to :
- make the crucial question prominent and clear, preferably summarised in the title, and
- include just enough context to make the difficulty understandable and well defined, but not so much that it obscures the crucial question or that reading it becomes a chore.
The advice to those who answer also needs to be more prominent, in particular encouraging them to use comments to ask for clarification and further details, rather than to post outline solutions.
(See : The practice of answering a question in its comments area.)
As I have suggested in answer to another Meta question, perhaps a very succint reminder of site policy/standards could be incorporated into the question/answer-posting process.