People. Stories are made by their characters, of course, but it's important to remember how your characters really are the lynch pin in your stories: without a three-dimensional character, no matter how compelling your plot is, it all falls apart. A good story has at least one character who feels whole and has all the elements of a real person. That means the details, such as physical appearance and likes and dislikes, are present, but there is also a sense of the character as an enduring personality.
Place. You've got to orient your reader in a time and place. Stories that really stick with us often have a strong sense of place, but that doesn't mean it has to be an exotic locale -- just imagine the place with all of your senses and give us a sense that the character is occupying a real space, not just floating, isolated, in the void somewhere.
Plot. Finally, you can't forget that what makes a story is that it has a plot! Many beginning writers make the mistake of forgetting plot entirely. They fashion elaborate character sketches and may have some nice description, but in a story some change has to take place. There has to be a reason we're reading the story. So make your reader wonder what happens next.