Composition/Short-Story

Few weeks back, our class did a narrative essay. We were supposed to write between 350 words and 500 words. We were given 3 prompts and a picture. I chose the first prompt and wrote a essay based on it. After my teacher had marked it, he gave some remarks. He said that I have an unclear story logic, vague descriptions, repetitive phrasings and inconsistent verb tense. I would try to improve in those areas and try to make sure it would not happen again. Recently, we just had a composition test and I hope that I can get good grades.
My teacher also said that a short story does not always need to have a moral lesson and not always be about a serious subject. A short story need not have a proper plot and the language used will not always be of a high order. My teacher said that a good short story must compel reader's attention from start to finish, must have a meaning that goes beyond the story itself and must affect the reader at the level of his innermost feelings.