Characters are what make the story. You have to have good characters or the story won't matter. We need to care about these people and what happens to them. I would bet your favorite movie has interesting characters that grow and change through the story.
Boring people don't sell books. We all know too many boring people in real life. We want a chance to escape into a more interesting world for a while. That's why billionaires, princes, aliens, shifters, pirates, historical, and motorcycle clubs are all popular genres. We want something new and original in our lives.
The best part is that you don't have to come up with a brand new character all on your own. You already have hundreds of them in your head.
Think of your favorite movie. I'm guessing you have a favorite character. They probably have something interesting about them. They probably have someone that they interact with that is interesting too. There is a relationship that makes it fun to watch. The way they react to problems speaks to you.
You can have a Mary Sue (someone with no real characteristics) as a main character, but only for self insertion. Think of Twilight- most people don't really love Bella, but we can easily insert ourselves into her head. She's a blank character. If we were reading this from someone other than Bella or Edward's point of view, we wouldn't see why Edward is so enamored with this very normal/boring girl. She could use a little more humor. Or a hobby. Or something that makes her stand out more than just she smells really delicious. We can't love her based on looks/scent/can't read her thoughts alone. We need to like HER. Not her attributes.
Being pretty isn't enough. Being handsome isn't enough. We need some flaws. We need something that we can connect with.
Let's create a character for a book. Let's call him Joe.
Joe is prince charming. He's handsome. He's rich. He's in the perfect age range.
Do we actually like Joe? Would you talk to him at a party? Would you set him up on a blind date with your sister? What kind of date would they go on?
We need more. He can be handsome. He can be smart, but we need to show that intelligence, not just say it. Instead of “Joe was smart” we need to say “Joe sped through his advanced physics homework. He didn't even need a calculator.” We should also clarify if he's book smart or street smart.
Then we need a flaw. It doesn't have to be something terrible, but something that trips them up. For Aladdin, he is a street rat with too much confidence. For Thor, he's not all that bright sometimes. Loki is self-centered and a trickster. Edward Cullen likes blood. Mr. Darcy has way too much pride.
These flaws make the story much easier. Why can't Mr. Darcy find love? He's got too much pride.
It makes the character relate-able. If the character is too perfect, we can't put ourselves in their shoes. We don't care about them. The Stepford Wives are only interesting as plot devices, not as characters.
Your hero and your heroine both need a flaw. If their flaws clash, even better. Your hero has too much pride? Your heroine having some prejudice against prideful people is great. We have drama.
In creating characters, use what you know. Is there a friend that you adore? Can't stand? Why do you feel that way? Take them and make them a character.
Same with TV shows. Do you LOVE Dr. McSteamy? Why? What makes him real to you? He's kind of an ass, but there's something charming about him. Use that.
There are so many amazing characters out there. Use literature (Pride and Predjudice), TV (Grey's Anatomy), Movies (Disney Princesses) and make them your own. Make Disney's Mulan meet Mr. Darcy, but they're on an alien spaceship. Maybe Arya Stark should have a meeting with Marvel's Loki, but they're both high powered business lawyers.
Imagine the possibilities!