In the early days of TeX.SE, the same question came upthe same question came up, and I think Andrew Stacey's answerAndrew Stacey's answer is a good one:
- Only ask the question if when reading it you think, "Hmm, I'd like to know the answer to that one too.".
- Only ask the question if it hasn't been satisfactorily answered.
- Re-ask the question rather than just cut-and-pasting it.
- Link back to the original question.