A lot of people find it hard to write a really good story in a small amount of words. I don't have that problem. I once wrote a story that had six sentences and make people cry. Let me tell you something, it's all about the amount of detail you put into the story. With a regular sized novel, you can span out the detail within chapters to keep the readers, you know, reading; but you can't do that with short stories. The readers need the information and detail near the beginning so they kind of understand what has happened in a short bit of time.
If there's one thing I should say about writing short stories is, just let the story write itself. Don't plain anything, don't outline, just let it flow. It's how a good story is supposed to be written. Don't think, just write, you can get the rough edges out later.
this is where i ramble; have fun