Setting is the most important decision writers make. Because it needs to be made the start of the manuscript. Other decisions can be made during the writing process--characters added and deleted, voice reworked to become more compelling, the plot twisted and turned, even endings can be rewritten. But setting is the foundation of the book. If I think about some of the most famous books in children's literature, I realize that they wouldn't be the same without their settings. Imagine HARRY POTTER without Hogwarts, the WIZARD OF OZ without the City of Oz, HUNGER GAMES without the Capitol.
I write realistic fiction, so I am not creating fantasy worlds or dystopian societies, but I do have to choose certain things to establish setting, such as the time of year the story takes place, where the main character lives, and one of the most important things for writers of literature for children and young adults--whether the story evolves during the school year or during the summer. In my first book JANE IN BLOOM, I wanted the most pivotal scenes in the book to take place during the summer, so I began the book in the early spring and carried it through summer to fall. In my latest release, SILENCE, the book takes place in a short time period and each day is significant so the dates had to be calendared and marked by me to countdown to the crucial day in the book. I also wanted the main character Stella to have to struggle with the issue of going to school because it would have been easier for her in the summertime, so I set the story during the school year.
I spend a lot of time thinking about my character's rooms. In SILENCE, Stella has Broadway posters all over her bedroom walls. I chose this description because I wanted to share something about Stella's dreams but then I also use the posters to show how painful it is to see them when her dream is shattered. In JANE IN BLOOM, I created a bathroom that connects Jane's room with her sister Lizzie's room and this connection is central to the development of the story.
If you are writing something new, take a moment to think about what time of year it will be and why. Decide what your main character's sleeping space is like, and how you can add personal touches to help the reader connect with your character but also reveal something about him or her. And whether your book is fantasy or dystopian or realistic fiction--choose whether your character is attending school and how will this help or hurt your plot and character development. Try different versions of these things to see which fits. When you find it, you'll know!