I don't know about you, but I really don't like the slushpile. And for the most part, if we're sending out our work, we're going to have to deal with it. It's not fun being in the slushpile either. That said, there are some things we can do to improve our odds of getting out of the slushpile.
For example, reading the guidelines. Sure it takes some time to find 'em. And sometimes you may find multiple sets of guidelines and have to decide between them but the closer you get to sending a publisher (or agent) what they want, the better your odds are. I don't know how many times I've heard agents and editors comment about people sending them queries for genres they don't represent. That's automatically gets your work discarded.
Sending an attachment is also another way to get your submission discarded. Yes, there are some places that want things as an attachment but most folks don't. It's just to risky.
Pink, swirly, 18 point fonts are generally a no no too. :-) Don't laugh, I once got a submission like that. There's a reason it's called standard manuscript format. It's the standard expected.
We all know our submissions need to be as error-free as possible. Don't rely on spellchecker to catch all your errors. Get someone else to look at your work. Or, if that's not possible, start reading from the end and work your way to the start. Yeah, it's strange but this way you aren't focused on the story, you focus on the words.
One of the many things we can do to better our chances of acceptance is to read several back issues of whatever publication we are submitting to. For fiction, this gives us the chance to get a feel for the publication. For example, just because it's a mystery magazine doesn't mean they will publish a cozy mystery. Maybe their focus is on hard boiled detective stories. You won't know that if you don't check 'em out. In non-fiction, reading back issues is a good way to see what type of articles they've published in the past, the tone of the publication and if your piece will fit or not.
Marketing research is one thing many writers don't like to do. It's time consuming, boring, and often you find more places your work doesn't fit than places it does. It's a necessary task though.
Want to by-pass the slushpile? Then go to writer's conferences. Talk to agents and editors. Having your work requested is like going to the head of the line. However, don't say your work was requested if it wasn't. They remember what they ask to see. You can always include a line in your cover letter saying you met them at such & such conference and enjoyed chatting but never lie to 'em.
Thing is, the more work you do before submitting, the better results you'll get. If you have to be in the slushpile, make your work stand out, in a good way.