1. The main character should FACE a problem/challenge and not BE the problem. Having a main character who is deeply flawed and whom you will "fix" though the story plot does not work for young people. It feels lecture-some (at worst) and fails to connect with the reader (at best). Like adults, young people like main characters they can relate to and admire. And just like adults, most young people do not consider themselves selfish, mean spirited, or spoiled. Sure, some actually ARE...but they still think of themselves in positive ways. It's just human nature. So if we create main characters who are selfish, mean spirited or spoiled - we create characters that the reader cannot connect with. And that makes a story fail.
2. The main character should face a problem/challenge that cannot be ignored. Your main character needs to have pressure to act. And since you're creating an admirable character, the character will act in a way he believes/hopes will solve the problem in a positive way. For instance, if your main character faces the problem of having something in his room in the dark, that's not something he could ignore. He couldn't just roll over and think...well, whatever it is, I'll just ignore it. Kids aren't wired that way. So he'd have to try to find out what's in his room and do something about it. So create a problem that forces positive action. And create a character you like enough that you're first choice for what he/she will do won't be a spoiled child action.
3. The plot will follow the actions of the main character on the problem. Overcoming must not be easy. The main character needs to pull upon something positive in him/herself in order to solve the problem. He/she may need to be unusually brave, or unusually compassionate, or unusually clever (or some combination thereof). It is by pulling upon that reserve inside him/herself that the main character will grow and change.
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