I'm preparing my first novel. I'll be writing during the National Novel Writer's Month challenge to write 50,000 words in 30 days. I'm pondering characters right now. I have an in-depth analysis of the characters we'll see the most, but what about those minor characters - do I really need to go into the same depth of development? If not, what are the essential elements I should hit for these characters?
All primary characters have to be believable and carried out throughout the story. Secondary characters are basically used to highlight the primary characters more; make the plot move smoothly and give an edge to POV when it is impossible to do so strictly using primary characters. Any other characters are not as important and I will often use them and describe them to enhance an issue pertaining to my primary characters. Eg. Primary character: Evan; secondary character: his best friend Steve; minor character: their history teacher, Mr. Byrd.
Where you would go into depth of developing Evan's character, you would mainly focus on the friendship of Steve and Evan and how it relates to the plot. Where we must know all about Evan, we only need to know the things about Steve that would connect us to Evan. As for Mr. Byrd, we need to know nothing about his background, but only that which connects him to the plot. It doesn't have to directly relate to the primary or secondary characters but can, if need be.
Further eg. A story would revolve around Evan and his discovery of treasure involving a famous tourist spot in London. He plans an adventure to acquire the treasure and uses his best friend, Steve, and his knowledge of history to figure out the best possible location based on historical clues.
You will need to outline Evan's character in great depths, briefly outline Steve's because the focus is on his knowledge of history and how Evan will use it, and not on him. And then when both discover that Mr. Byrd holds the key, you don't need to know anything about Mr. Byrd in great depth since he's more than likely to be seen only briefly in the story when the boys try to get the key from him.
I hope this helps. Good luck.