Character is first and foremost. If you don't have the right characters populating your story, then no one is going to want to produce the script let alone read it.
A hook runs a close second in scripts... some would say it is no.1 and the characters come out of the hook. Each to his/her own.
Timing and tempo are essential, too. You have to keep the reader's rear in the chair long enough to keep them reading all the way through the script... even if they have to pee. Give them material that will make them forget that urge!
Plot, time line, characters (who are likeable or not), problems, and, I hate to say it, but cliffhangers. I absolutely hate cliffhangers, but they're what keeps the story going and the reader interested.
Plot, characters, setting, and an open mind.
The ingredients in my story giving it a unique and amazing flavor is Imagination, inspiration, creativity, love for what you do, a dream, and a hint of Yourself.
I'm always looking for new ways of writing, so I will start with the most basic premise and add a simple character. The ingredients are added later depending on which direction the story takes, but good characters combined with an unusual situation generally add to a great story. I never discard any ingredient when writing as being open minded ensures every opportunity is available.
Characters and plot. Very important though the element of surprise should always be considered.
People have to want to turn the page, they want a picture in their mind, an adventure to go on.
The answer is as varied as there are kinds of stories. Usually there is always some kind of catharsis or resolution from conflict, whether implied or not. It's hard to find stories without this. Homer obviously sets up ingredients that are useful for many writers and poets throughout history, extraordinary characters under pressure committing acts of heroism, whereas Joyce's Ulysses is an Odyssey in one day, of ordinary characters perhaps making mistakes and acting very "mortal." The key thing, is whether the story is ancient or contemporary the reader is involved somehow. I would become worried if a young writer asked, "How do I write a great story?" because he might try to follow one formula slavishly without realizing the plethora of story techniques available for him.
Dreams, Imagination, and a touch of reality.
You have to paint a clear picture. Staying on topic and not losing focus is vital.
Entertainment is the key ingredient of a story. The next most important item is education. Many of my stories contain footnotes to events or places being discussed or discovered by the story's characters.
When I used to write stories for myself I would have said 1. A snappy beginning, 2. A clever plot and 3. A satisfying conclusion. Of course I also liked to write satire. That was probably my favorite hobby. Then I would start with a current topic or controversy, turn it on its head and wrap it up with an ironic twist.
I'm going to avoid the "goal motivation conflict" answers other authors have probably given.
For me, what a story needs is emotion. Showing, not telling. Vivid imagery. We authors are "painters with words." We invent a world the reader imagines. Therefore, this world shouldn't be two dimensional. It needs to move me. It needs to make me transport to that world. I want to be so engrossed that the book falls away and it's like I'm there. I want to laugh and cry with the characters. The books that can make me do that are the ones on my keeper shelf.
As a humour writer, the basic ingredient is knowing my characters very well, putting them in situations, and mixing that with how they react.
Characters aren't always funny. Stories are often serious. It's the way a character reacts to a situation that can be humorous.
I don't write stories, I write pieces.