We've all heard it before, but it's always a good reminder. Before you submit a piece, check the guidelines. Thoroughly. Read and re-read them while looking at the piece you plan to submit.
Recently, I received a rejection, although the editor did ask for a rewrite. I had looked at the guidelines, but missed a critical point. It was a non-fiction piece for which they required three sources. I had three sources, but they were internet based. The line I overlooked was "Bibliographies cannot solely rely upon internet resources." I shouldn't have missed it - it was in bold face - but I did.
Mistakes happen. We're anxious to push the send button, but sometimes our haste only creates delays. Now, if I wish this editor to consider my article, I need to go back and seek out additional resources. Had I paid attention to the guidelines, I would have found the correct reference materials in the first place.
Guidelines are created for a purpose. Each editor has her own preferences. If you want your work to be considered seriously and professionally - read those guidelines.