There will probably be at least two blog posts on the subject of characters since when writing your story the characters are vital to make the story come alive. Of course you have a character in mind and maybe you will learn more about them as you write the story but there are some influences. That's why I did the where, when, why and what before I started to show my character. How do these parts of a story shape the character.
When looking at when a story takes place, the writer has to consider the nature of the character. One doesn't plop a contemporary person into a historical, or someone lacking curiosity into a murder story as the main character. The year, century must be considered when developing the characters in a story. They must be appropriate to the time period where they exist.
Looking at the where. Now you might put a southern belle on a space ship, notice I say may but you wouldn't want her to be the pilot. Where the story takes place has much to do with developing a character. A nurse or doctor fit into a story with a medical influence but having them in a story where their profession gives no insight into their nature doesn't work.
What a character desires plays very heavy in their character development. If they have everything, what is there for them to desire. So look at the character's wishes and hopes to help form their character.
The same goes for why. Why does Mary want Joe? Why does Susan want revenge/ If this isn't know before the character steps onto the page, they might fall flat. Why is the aerator of the story or maybe the yeast that makes the story rise.
So look at all these things. Next week there will be more you need to know.