It would be good to have questions put into an initial review queue where users could edit (with 2000 rep) or vote to close or release (with 3000 rep), but that would be a major change which would need a concrete proposal and support on Meta.ELU before going to Meta.SE for support. It's a major change to the Stack Exchange model, and it could be difficult to make work.
So we have to work with what we have.
As Mick has intimated, the gatekeepers are those with at least 3000 rep as they can actively vote to close poor questions.
All you need to do is check the close reasons and the on-topic list. Dan Bron's heuristics which he listed in a comment are the short form:
- Would five minutes of an internet search answer this question?
- Does it seem like the OP opened a dictionary or did any research at all?
- Is this a non-native speaker who would be ultimately better served by the teaching experts at ELL?
- Is this a question which would occur to, and be interesting to, native speakers, or would native speakers intuitively and immediately know the answer off-the-bat?
Questions on these subjects are explicitly on-topic:
- Word choice and usage
- Grammar (but note that this is a narrow definition of grammar)
- Etymology (history of words’ development)
- Dialect differences
- Pronunciation (phonetics and phonology, dialectology)
- Spelling and punctuation
Even on-topic questions can be closeable if they are poorly written or do not take account of guidance contained in the tag popups. If the question fails any of the initial litmus questions, then it's failed.
Questions on these subjects are explicitly off-topic:
- The meaning of words, or synonyms for words, unless you have first looked them up in a dictionary or thesaurus. See the Help page for suggestions about simple and basic questions.
- Proofreading ("Is this right?", "Are there any mistakes?"), unless a specific source of concern is clearly specified. See the Help page for hints on checking existing texts.
- Writing advice (see Writers.SE instead) or critique requests
- "How to improve my English?" (this is not constructive anyway)
- Translation and non-English languages — please see the translation tag info for details
- Naming, including naming programming variables/classes
- Criticism, discussion, and analysis of English literature
- Jokes that do not rely on the English language
Other questions can be deemed off-topic:
- Does not demonstrate sufficient (or, often, any) research
- A single-word- or phrase-request without sufficient detail
- Not about the English language: perhaps it could go to another site (you need to raise a custom flag for these, but can also write a custom close reason)
- A good question about English but which is asked by someone who needs a didactic response: nominate this for migration to ELL.
Don't recommend migration for poor questions — no site deserves to be given poor questions. If you can improve the question so it won't simply be closed on the destination site, do that first. If the question is unsalvageable, then it should simply be closed on ELU, perhaps with a comment that another site might be better for the question's subject-matter.
And other questions can be closed for other reasons:
- Another question contains an answer which answers it
- The question is fundamentally unclear
- The question is too broad: either it addresses a topic without being specific about the exact problem, or it asks more than one thing, or it invites a list without specifying any criteria for choosing an answer
- Answers to the question are entirely subjective
What to do when considering a question for answering
Ensure that it is not off-topic or otherwise closeable. If it is, vote to close it. Even if you do this, you could help the asker by leaving a comment addressing his question.
If it's on-topic, write a good answer, in particular paying attention to corroboration for what you write. Without it, your answer is just opinion. It needs to be backed up (personal experience is OK; published corroboration is better).
Always vote. If a question does not show research, downvote it. If a question is useful and asked well, upvote it. Votes are used by the system to help determine what should happen with a question: by casting votes you are helping the system do its job, and helping the community by showing which are good questions and which are not-so-good. Don't withhold — or cast — a vote simply because a question is asked by someone with low reputation.