okay, let's try to sum up some basic guidelines!
1) No using your own subs!
2) Taking advice from Scrasamax, you must use elements from at least three submissions, though using more is great.
3) Story must follow the basic story structure, that is to say it has a beginning, a middle and an end. No cliffhangers, thanks.
4) All elements that the story contains MUST be from submissions, unless it is an absolute staple of the genre (i.e. laser guns or generic spacecraft for sci-fi, dragons and taverns for fantasy)
5) Just so that we know what you're talking about, please give us a link to the subs you used!