This is a day late- sorry. It's been busy days...
Anyways. Character development. The best thing you could do is get to know your characters. Are they talkative like your sister? Is their favorite color white, like your best friend? Did your MC get into a fight with his/her mother and are now sulking? Or maybe they're thinking on their mother's words and regretting the harsh things said?
I challenge you to answer these questions on a piece of paper or a word document:
1. What is your character's full name?
2. Who is their best friend?
3. When is their birthday?
4. If offered a choice between eating a gallon of vanilla ice cream or going snowboarding, which would they choose?
5. You character has a choice between getting a pet rabiit, snake, cat, or dog. Which one?
6. How does your character greet strangers off the street?
7. How does he/she greet friends or enemies?
8. What is their favorite color, favorite book, and/or their favorite gemstone?
9. How many siblings do they have? Are their parents divorced/dead? Do they live with any other family members?
10. How do they treat their family? With affection or sibling rivalry or downright ignore them?
11. What does their room look like?
12. What are his/her hobbies?
Character development is easy and important in writing. Treat your characters like real people, and describe them like real people. And remember- people are more than one thing. They aren't just "talkative", or just "energetic" or just "rebellious".
It might help to stick to a "type" of personality though. You can't have your character talkative and rebellious but preppy and trampy as well, oh and she gets depressed often and while she's super curious, she's also apathetic... that's just confusing. A common, almost cliche one is the quiet, shy girl who is the heroine of the story. Another is the hot, popular guy who is too afraid too stick up for himself and is secretly a nerd at heart or something. You don't have to make them like that, but you might want to stick to similar personality traits. Unless that doesn't work and your character Joe is in a mental hospital or something.
That's pretty much it. Remember, no one is one thing, but no one is everything, either. To develop your characters, get to know them a little better yourself. After all, you can't describe someone you don't know, right?