1) Know the world you set your story in well. It will show in the quality of your story.
2) Use a single point of view rather than jumping between characters. Your space to develop multiple points of view is too limited.
3) A good way to begin your story is with a sign or herald. This can be a dream, or a vision, or an unexpected event. A portent. It foreshadows later events.
4) If your story has a mentor, try to break from the now cliché old man with beard image. Be imaginative with your mentor force.
5) A good way to finish a story is to return in some way to the beginning, the starting point.
6) Never finish a story with the words ‘She/he woke up and it was all a dream!’ That’s a serious let down!
7) Use your short introduction to sketch in the context of your story (especially if it is a part of an imaginary longer story) and your approach to archetypal story patterns (Vogler)
8) Don't forget that a good story will create a mood or impression. Use description to do that - description of the setting and characters