Your opening is the bate that draws the reader in. You need to have your reader wanting to read more as soon as possible. So unless you are writing for a well established market with odd tastes your opening needs to be short and sweet.

A good opening introduces the character, plot and basic dilemma ideally quickly and urgently. Great openings often jump right into the action starting with a scene where it's all happening.

For example: "Jack dodged around another tree as more gun fire sounded behind him. His lungs felt as if they were on fire but he kept running. I must make it to the border, he thought."

This is a lot more gripping than what Jack was doing a few hours earlier (eating beans on toast).

This is the meat of your story. When people talk about what you write and how to write it they are talking about what is in here. This is where you expand on whatever happened in the opening scene.

You need to develop your characters and take them on a journey so that hopefully they or the readers are different for having taken the journey.A simple story need be no more complex than a person learns a fact and then they react to the fact.

How they learn it and how they react and cope (or fail to cope) is what makes the story interesting.

With the very short story anything under 3,000 words you have no time for complexity. You can hardly afford many characters on your stage because the stage is so small. Ideally to make the story satisfying some twist needs to occur.

Now you need to end the story. This needs to have a sense of finality about it in terms of the tail you are telling but with shorter fiction it should leave you wondering "what will they do now".

With our fictional opening we had Jack running from people with guns. Our ending might have Jack meet his enemy only to have them say:

"So you see, Jack, now you have crossed the border I can not save you and you can not come back."

Depending on the body of the story this might be a lie, a crushing truth or an irrelevant nothing. The ending needs to fit with the middle and the middle must lead up to it. The ending needs to teminate the telling abruptly.

Don't linger.