Be creative man. Once you pick your pen up, your mind will be filled with ideas. Good stories always has a beginning , middle ( in which its up to you if you want to make it a love story or a suspense, its up to you. Write whatever you can think is best, i am good at writing stories and i usually right any of the types i have mentioned above.) , and lastly the ending. Your ending has to be like super cool, end it with a quote or umm.. if i would've ended the story with a suspense i which i'd like my teacher to figure out what happened in the end :P but its up to you really. Writing a Story is easy, Remember one thing, put anything that comes to your mind on that piece of paper. :) best of luck .
You can write a short story based on fiction or facts. Fiction can include stories like why the zebra is black and white while facts can include why the sky is blue. Make your story interesting by using humor or by going straight to the point and later elaborate the mentioned ideas.
Write about an experience in your life that took a big part in your life and changed your life dramatically. I mean you cam write about anything maybe write about something your interested in for example I like to surf I'd def write about that! :)