One good start could be a mysterious statement like 'The door at the end of the corridor was ajar, and a strange light seeped through.' It immediately grabs the reader's attention and makes them wonder what's behind the door. Another option is starting with an interesting character in an unusual situation, for example, 'The old man sat on the bench, his eyes fixed on a spot in the sky as if he was waiting for something that no one else could see.' A third way is to begin with a bit of dialogue that sets the tone, such as '"You can't be serious," she said, her eyes wide with disbelief.'
A great start to a short story can be a description of a vivid and unexpected scene. For instance, 'The town square was filled with hundreds of balloons, all floating in different directions as if they had a life of their own.' This creates a sense of wonder and curiosity. Also, starting with a conflict is good. 'He woke up to find his wallet missing and a stranger's note on the table.' It makes the reader eager to know how the character will deal with the problem. Or you could start with a thought - 'She always wondered what it would be like to live in a world without colors.'