If memory serves, there are some MO questions generating lists of good mathematical writing? If these do exist, I suggest you look at them, and think about what works and what doesn't. If it does not exist, I could imagine you asking for such a list, or focus it on a list of articles with well-written introductions.
I would support a (CW!) question asking not for advice about how to write an introduction, but for things that people like in good introductions. For example, I like "sign-posting", when you very clearly lay out what you are going to say before saying it. So that answers don't draw on, if I were asking the question I would specify that I was looking for one-sentence answers.
]]>