Though we don't generally strive to write flat characters, they are often necessary in a story, along with round characters. Take, for example, Mr. Collins in Jane Austen's Pride and Prejudice. A flat character, he serves a vital role in the story of how Elizabeth and Darcy get together, and he provides comedy, but his character stays essentially unchanged. (In fact, that’s part of what makes him funny.)
How do you go about creating round characters rather than flat ones? Creating complex, believable characters takes time and thought, of course, so get started by answering these questions for developing characters.