I try not to be insulting about the slush pile, in public anyway. I fail, pretty frequently, but that's another matter entirely. The fact of the matter is we've all been there, and it's a learning process. There are a lot of things I think most of us learn with experience, as we collect that folder of rejections and see what works and what doesn't. Still, I'm pretty sure we'd all like to skip a bit of that. So. Just for you, I've got a pithy ridiculous list of tips (because it's me, I don't know what else you expected).
1. Follow the bloody instructions!
Literally nothing as a reader is as annoying as having to wade through extra stuff you're not going to accept anyway. I know it seems cold, but if I've asked for something in a specific format it's for a reason and I don't have the time or the impetus to decide if you're special enough to be exempt from that. Nobody likes to be ignored, so don't set yourself up for failure by ignoring an editor's requests.
2. Nobody cares.
This one's a little cold too, but it's the truth. Unless you're submitting to a religious publication, I don't want to know about your relationship with whatever your deity of choice is. Unless I'm asking you for an anthology of poetry I don't want to know every place you've been published in the last six years. Unless it's immediately, inherently relevant to the thing you're sending me I don't care. If your cover letter rambles I'll probably skim it at best, and be less inclined to give your submission the kind of attention you'd like me to give it.
3. Nobody's story is good enough to survive not having an ending.
I've touched on this before, but it bears repeating. A lot. We've gotten some clever, wonderful stories we'd have been happy to publish, until they took a short sharp turn to the left and went off the cliff. Look at your plot, and imagine you're telling your best friend this thing that happened to you in the coffee shop down the block. How many times would they hit you if you walked off where your story ends? Then for the love of all things fluffy, fix it before you send it out.
4. Develop a relationship.
There isn't a publisher out there who doesn't have a twitter account, and a facebook, and... ours included. Hunt them down. With an account with your name on it, because I sure remember that stuff, and I'm sure other people do too. Especially independent or small press publishers. Reply to their tweets, create a relationship, even if it's based around pithy Star Wars one-liners. Find out if they have a mailing list you can be put on. Make yourself a real entity, a person who could possibly be depended upon for content. It's a foot in the door that will cost you minimal effort and no money.
5. Look at the date.
Up there, in the corner, that you wrote when you finished your final draft? How long ago was it? If you haven't changed, demonstrably, as a fledgling writer in the last two years we're gonna have to talk. If you finished that story four years ago and you're still sending it out with that date on it we really have to talk. Unless your Steven King...No, scratch that. Even Steven King changes as the years go by. If it's more than two years old give it another draft before you send it and change the bloody date on the thing.
6. Shotguns are good for hunting, not submissions.
We got a submission for The Golden Fleece. To the wrong email address. I stared at it for a good two minutes, utterly poleaxed. Not only did you not bother to actually read our guidelines, you didn't even look at them. Your sending me a story when you don't know what you're sending it to. You don't know who you're sending it to. In what wacky parallel universe do you live where crap like that works? Do you offer short-term vacation visa's, because I'd like to go visit somewhere my stuff could be published because I scatter-shot all over someone's inbox.
7. Know your market.
This should fit under that first tick up there, about reading the instructions, but apparently it's a separate thing. I don't understand people sometimes. It should be self-explanatory. Not "This journal is for unpaid dental assistants who like Anime. Gee, maybe they'd like my story about an old man coming to terms with his eventual slide into uselessness in the nursing home." Maybe they would, but probably not. If it's a publication for children your story needs to feature children--this is a strict rule, because small ones are less plastic with that whole suspension of disbelief thing. My seven year old still has to constantly check with me to make sure things are fiction--and for the teen market there's a little more play, but not much. There's not a teenager alive who thinks 40 year old dudes are cool. Unless they're Johnny Depp...and I'm not sure he's even still in his 40's so clearly he's a special case.
8. Don't be a d-bag.
Yeah, this is another of those self-explanatory ones. Here's the thing. In a book, you can get away with having a truly despicable main or point of view character. Maybe. If you're really good. You can sort of...Stockholm Syndrome us into liking them for other reasons. I'm not saying it's a thing to aim for, because its damn hard to pull off, but it can happen. For a short story market you've got like 2 pages, tops, and arguably like 2 sentences to hook the reader. There's not time to convince me Jack is a really great guy to spite the fact he talks about women like Ian Flemming's more misogynistic cousin (I say this with the full understanding I'm judging Mr Flemming entirely by the existence of a character named Pussy Galore and not having ever read a Bond novel).
9. No, you can't have any more!
Do. Not. EVER. Ask. For. Critique. Ever. Ever ever ever. Like seriously, even if by some small miracle they've offered it before. You aren't Oliver, shuffling up to the table for another bowl. Or you certainly don't want to be. Aside from being seriously unprofessional, I promise with a small press they'll remember, and be seriously unlikely to consider future submissions you send them.
10. "We're drift compatible!"
Everybody tells you to find a crit group. I know. I know. But here's the thing. A crit group, or a couple of friends you're comfortable making a little circle with--even if it's a triangle--will do more for your writing than nearly anything, except possibly a decade of time and a published mentor. Not only are you likely to start learning the things you do wrong--and stop doing them--I promise learning to edit other people's work and give constructive critique will make your work immeasurably better. There are tricks for this, but that's a discussion for another day. The short version is find people you respect as creators, who understand what you need out of this relationship and are marginally willing to give it to you.
Alright, that's all I have for wisdom to impart, mes enfants. I bid you, go and create. Vite vite.