In this type of story the main character's wish must be something that seems almost impossible to achieve. The main character may try once or twice to fulfill his wish, but he must fail so miserably that the reader sees just how truly difficult it would be. The main character also may simply wish without making the effort because she thinks her dream is unattainable.
There are two types of Wish stories. In one the person gets what she wants because of who she is. The poor girl wants to marry the gallant prince and when she has a chance to meet him he is so impressed with her good qualities (which the rich women he has met lack) that he wants her to be his bride.
In other wish stories, the main character gets what he wants because of what he does, but it must be unrelated to his original goal. He may loves sports and therefore wants a summer job at the local minor-league baseball stadium. He knows it's a longshot to get a job there, because he is under eighteen, but he did set up an interview.
On his way to the interview, the boy may stop to help someone change a tire. As he gets dirty and sweaty and late for his job interview, he talks to the driver. The driver is opening a sporting good store, but he is worried no one will show up for his grand opening. The main character misses his job interview, because he is late after helping change the tire and talking so long to the store owner because the main character is so interested in what the store owner has to say. The main character finds out that someone else, much more qualified, got the job with the minor-league team.
The next day the main character goes to the grand opening of the sporting goods store. There are few people stopping by. The main character suggests to the store owner, who remembers him from the day before, that he could help the store owner by dressing in various pieces of sports clothes, going outside and carrying the Grand Opening sign that is just sitting in the window. The owner agrees. The Grand Opening is a success. The store owner offers the main character a job as a sales clerk at the sporting goods store and the main character happily accepts. Though it's not with the minor-league baseball team, he has a sports-related job.
The wish in this type of story must not be filled until the very end. It must be a suitable one for the main character. The main character must be one the reader likes and will root for.