The requirements for a short story competition can vary. It could be that you have to submit your story by a certain deadline, stick to a particular style of writing, and make sure your story hasn't been published elsewhere before.
Many Hindu short stories teach about dharma. For example, in the story of Rama, Rama always follows his dharma, whether as a son, a husband or a king. This shows that one should always uphold one's duties in life.
To win, you need a compelling opening to hook the judges. Develop complex characters they can relate to. And, proofread carefully to eliminate any errors.
First, come up with an interesting idea. Make it unique and something that will catch the judges' attention. Then, focus on creating well-developed characters and a clear plot. Also, pay attention to your writing style - keep it engaging and easy to follow.
For Vishnu, there is a story where he took the form of a fish, Matsya. The world was about to be flooded, and he guided a pious man named Manu to build a boat. Matsya then towed the boat to safety, thus saving life on earth from the deluge.
Well, to judge a short story competition, you first need to look at the plot. Is it engaging and coherent? Also, check the character development. Are the characters believable and well-rounded?
One story is about Ganesha. Once Shiva was away and Parvati created Ganesha to guard her. When Shiva returned and tried to enter, Ganesha stopped him. Shiva, not knowing who Ganesha was, cut off his head in anger. Later, realizing his mistake, Shiva replaced Ganesha's head with that of an elephant.