Tip of the Week: Do not make your submission impossible to open.
Yesterday while I worked, I watched some of the others sort slush. Most of the submissions were in envelopes or boxes and you could get into them with a paper opener. Buuuuut, there were a couple with special arrangements. One was wrapped like a present. I was surprised since I thought that the post office only shipped things wrapped in brown paper. Another box had every inch covered with tape. Scissors wouldn't even go into it. We had to go hunt up a box cutter. Now, these are little things that don't affect the quality of the submission. However, it did affect our mood. And you never want to start getting the people handling your manuscript in a bad mood.