Nayad Monroe writes the appropriately titled blog 'Never Forget That Writers Are Insane'. She lists things she has learned from her experience reading unsolicited submissions. It's worth checking out if you need some guidance on how to stand out in the crowd.
My personal favourite was number 5:
A person who has read thousands of story submissions doesn't have any patience left. I'm very sorry, but it's true. I get fidgety. I've read the beginning of so many stories, and I've seen so many of the common ideas that come through, and I've been so disappointed by stories that started well but ended badly. You might not believe the enthusiasm I feel when a story shows me something new, something expressed beautifully, with ideas thought through so that I don't get distracted by implausibility. I LOVE an excellent short story. I have low tolerance for a mediocre one.