1. Use the time of a total stranger in such a way that he or she will not feel the time was wasted.
Make sure you actually have something important to say. Recently I waxed poetic, badly, about what Story means to me. Nicola Griffith, another fine writer, said something about the writer's goal and process. I think it applies here:
When I write, dear reader, I don't want to build a careful tale for you to discuss with a smile in a sunny place, I want to own you. I don't want to be The New TV Series, I want to be pornography: to thrill you so hard you're ashamed but can't help yourself crawling back for more.
2. Give the reader at least one character he or she can root for.
Some people call this sympathy; I call it empathy. I don't have to like your characters, but I should want them to get everything they deserve.
3. Every character should want something, even if it is only a glass of water.
Every character should want something, not just the protag and antag. This does two things: it layers and enriches a story, and it forces you to cut any characters that aren't tied into the main action by their goals. I write and read upwards of 10 hours per day (and night). I'm all for cutting.
If achieving the goal contains an ironic twist, all the better. Robert McKee says about irony:
...in story, irony plays between actions and results--the primary source of story energy, between appearance and reality--the primary source of truth and emotion.
I would expand upon that to include: irony plays between character and goal--the primary source of growth and development.
4. Every sentence must do one of two things -- reveal character or advance the action.
The delete key is your friend.
5. Start as close to the end as possible.
I'd guess there's room for about a paragraph of backstory in the short form. The best way around excessive backstory is to employ characters and situations that your reader will instantly recognize and identify with emotionally.
6. Be a sadist. Now matter how sweet and innocent your leading characters, make awful things happen to them -- in order that the reader may see what they are made of.
Your story is boot camp, your characters are pale new recruits, and you're the drill seargant. After all, a good story basically asks its readers to go to war with its characters.
7. Write to please just one person. If you open a window and make love to the world, so to speak, your story will get pneumonia.
You can't please everyone all the time.
8. Give your readers as much information as possible as soon as possible. To heck with suspense. Readers should have such complete understanding of what is going on, where and why, that they could finish the story themselves, should cockroaches eat the last few pages.
This ties in with backstory, too. I just read a story last night in which the big reveal causes the characters to engage in a distinct "as you know, Bob" conversation. This was because the reveal was actually the premise, and an intriguing one. Had I known the "secret" that motivated the characters, I would have understood why they were doing what they were doing. As it was I floundered and gave up. Well, actually, I went and read the ending, realized it was structured poorly, and sent my Dear John letter.
This flawed structure of using the premise as the reveal is common. It also ties right back into the first rule: Use the time of a total stranger in such a way that he or she will not feel the time was wasted.
Resist using your premise for suspense. A good story relies on action and reaction to the premise for suspense. The premise should drive the characters; the reveal, the suspense, should most often be what the characters will do about it. (I say most often, of course, because writers break this rule with great success all the time. Just not very often in my slush pile.) I'm a simple editor with simple needs. If you give me an intriguing premise that drives interesting characters to react in interesting, kick-ass ways, then you'll likely sell me a story.
Have faith in your premise. Trust that it will not waste the reader's time. Let it shine in the first paragraph; don't hide it behind a veil of vague dialogue, unmotivated action, and inconclusive narrative. In fact, often the best place for the premise is the first paragraph, or at least the first page. This is all about structuring, but it also may be about quality. If you feel you must hide your premise from the reader, then it may not be as strong a premise as you thought.