Some examples that seem to work for me.
Provide a detailed analysis of the question.
Asking why the question doesn't do the preferred method.
This can be difficult to get right. If you come off as mean, people will down-vote your answer, instead of up-voting it.
Post an answer that does what the OP wants, but the way it should be done.
Specifically, not what the OP is asking.
Post multiple answers that are significantly different.
For example to the question Regular Expression to match valid dates, I posted three different answers.