One thing that I find gives me a lot of rep, is providing a detailed analysis of the question.
Another thing that seems to work for me, is just asking why the question doesn't do the proffered 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.
I also like to just post an answer that does what the OP wants, but the way it should be done. Not the way the OP is asking.
I have also just posted multiple answers that are significantly different.
For example to the question Regular Expression to match valid dates, I posted three different answers.