I like the "Questions that may already have your answer" suggestion box which I think prevents some duplicates. At least for me.
I suggest to take this further. E.g. on StackOverflow, questions titled "XY not working" are increasing, but not really welcome in that way. IMHO such a title is not specific enough and most of the time won't contain any error messages or other hints to answer the question. So the usual things take place: The question gets downvoted and comments are appended like "define
not working?", "can we have an error message please?" and so on.
An obtrusive alert for certain conditions before posting the question – like gmail does when you wrote '[something] attachment' and haven't attached a message – would be a nice feature.