Do these three things to get to the top of the slush pile:
The place has a style sheet. Use it. They say they want your MS in 16.5 point Papyrus italic with 0.8 inch margins all around, guess what you're doing before you send it off? Save As, reformat, send it. In the absence of a specific guide: Courier 12 pt (Times New Roman if you must), double spaced, align left, tab 0.5 at each new paragraph.
Check the word count. Don't submit novellas to 2500 word short story venues. BTW, you format the MS in that old style above because the question isn't literal words. Courier 12pt double spaced gives you 250 words per page for typesetting purposes. 2500 words is 10 ms pages, 5000 is 20 pages, etc.
Don't send your romance to Analog or your war story to Harlequin. If it's a cross-genre story, be sure there's enough of what the publication is focused on to interest them, but breaking through is hard if that's not something they usually do.
That's basically what every single editors' panel at every con I've ever been to has boiled down to. And invariably, someone tries to get up and argue with them, not realizing it's not a discussion.
Bonus tip: Don't be in any way cute in your cover letter. Just the facts/Luke Skywalker's message to Jabba the Hut in ROTJ.
Enclosed/attached is my story <Title> for your publication <Magazine>. It is x (rounded to the nearest 500) words. I can be reached at <email> (that you check regularly and isn't likely to dump things into spam) and <phone>.
(If submitting a hard copy: The manuscript is disposable. A SASE is enclosed for your response./A SASE is included for return of the manuscript and your response.)
Thank you for your consideration.
If submitting a novella length piece or greater, a brief and complete summary is appropriate.
In the midst of an interstellar revolt against an evil galactic Empire, vital weapon plans fall into the hands of a farm boy on the edges of the galaxy. With the help of an aging warrior from the Old Republic, and a smuggler with a dark past and his imposing alien copilot, the four set out to deliver them to the rebel forces but are instead flung into a rescue mission to save the beautiful princess who stole the plans as worlds are destroyed by the might of the Empire's weapon, the Death Star.
Captured by the Death Star on route to deliver the plans, they manage to escape the base with the princess, the old warrior sacrificing himself to make this possible. As the Death Star approaches the rebel base, they use the captured plans to stage a desperate final stand. In a fierce space battle of single-pilot ships over the surface of the moon-sized weapon, the farm boy manages to make the critical shot with an unexpected assist from the smuggler, destroying it.
Never under any circumstance put a cliffhanger into a query letter summary. There is no faster way to get the entire MS binned than doing that.
PS "Top of the slush pile" means into the top 25% of manuscripts received. Three quarters of the submissions don't take the trouble to do even those three basic steps.
Now, that still means 25/100 submissions or 250/1000 submissions, but it still improves your odds and forms the basis for starting a relationship with the publisher for the next piece you send them.
PPS This is obviously about prose. Poetry certainly has its own submission rules, and I know none of them. If you're writing poetry, find out what they are.
