Keep in mind that this is a group for readers, not writers. This being the case, submissions should generally be done via note, as you should be "submitting" someone else's work, not your own. If you are a writer as well as a reader, and you feel that one of your pieces fits the criteria below you can, of course, submit it the normal way.
We are looking for writing that is:
Free of mechanical errors.
Ideally, there should be no grammatical errors, typographical errors, word choice issues, spelling mistakes, omitted words, or anything else of that nature. Realistically, even the best of writers miss things from time to time, so if there are one or two small issues (of the sort that occasionally even appear in published pieces) it won't be a deal breaker. If, however, it seems that the writer either hasn't bothered to proofread their piece (if they can't be bothered to read it, why should we?) or doesn't understand some basic usage issues (using the wrong their/there/they're even once...) we don't want it.
a stand alone piece.
As readers we want to read the whole story, not chapter 4 of a story. If you want to suggest a chaptered piece, we'd prefer if all the chapters were available so that our readers can read the whole thing. If the rest of the story isn't available, but the chapter you want to suggest can stand on its own merits (ie. is a complete story in its own right), as is sometimes the case with introductions and prologues, you can still submit it. Generally, though, we'd prefer stories that only take one deviation to tell.
Basically this means no fan fiction. Fan fiction is a copyright grey area from both a legal and a moral standpoint, and we don't want to get involved. I know that, personally, if someone started writing stories with my characters without asking my permission I would hunt them down with neither mercy nor remorse. The quality of the writing is irrelevant in this situation, it's all about respect for your fellow artists.
All writing serves a purpose. Whether it is to evoke a mood or emotion, or to entertain, or to provoke thought, or persuade, or to communicate and inform there is a purpose behind everything that is written. By well written we mean simply that the purpose of the piece is clearly and successfully accomplished. If it is meant to entertain, was it entertaining? If it was meant to evoke an emotion, was the emotion evoked? This is more subjective than the other criteria, but by applying it in a reasonable manner I hope we can avoid too much controversy.
I can't really think of anything else to include here at the moment, although I'm sure more things will occur to me as we go forward (I'm pretty new to this). If you've any suggestions for selection criteria, or anything else for that matter, just drop the group a note.