I have kids. LOTS of kids. So when I'm brainstorming/outlining a book and I need to form a character I often find an excuse to snuggle on the couch with a baby and watch a Disney movie. Disney characters are sound, living and breathing good characterization that create solid plots. They have great conflict, might be a tad predictable, but the characters are consistent and compelling. You know this. They are why Disneyland exists.
And why you have a t-shirt stashed in your closet of your favorite Disney character.
The one that is YOU.
I have used several different personality tests to help me cast a solid character--but they are time consuming (for me) and don't often work because I find I haven't really established who that character is yet. It's like putting the cart before the horse. So, for me, the Disney princess (or prince or toy or car or animal) personality profiling works as a great starting off point. After that I can ask my character a hundred questions like where they grew up and what their most embarrassing experience was, and what was their first kiss like--but until then I need a general, generic personality-type I can gravitate toward, test how they would respond in certain situations.
Great books and movies reflect the same stories all the time, you just might not see it because it puts a unique twist on it at the same time. If Elizabeth Bennett were a Disney Princess she'd be Belle of course, and Mr. Darcy would make a fabulous Beast. Belle in Twilight would be Ariel, sneaking around her parents and trying to hook up with someone different. She'd have to trade not her voice, but her humanity to be with. I saw a movie just the other night, "Ever After," and the main character is Danielle/Cinderella, but her Disney Princess would not be Cinderella, but Tiana (my personal favorite) with the you-can-accomplish-anything-by-working-hard attitude.
And FYI, Disney does this too. Lightning McQueen spoiled rich kid is a lot like Prince Naveen--just different twist.
Best place to start is ask questions. Like, for the post-apocalyptic zombie book you're writing, what would happen if Jasmine was there? Grown up pampered her whole life with a giant tiger for a pet?
What if Tarzan was dropped on an alien planet as a baby, learned to speak the language of Martians, and later was visited by others of his race?
Wait. That's Superman.
Seriously, the inspiration is limitless.
Also, look at why those characters work. They have backstories, and relationships with family and friends. If we didn't know that Meg in "Hercules" was used and cheated by the love of her life we wouldn't be drawn to her and root for her when she does bad things. Your characters need backstories and lots of relationships with other people to help define who they are, to give them shape and form.
Disney body snatching is not the solve-all, end-all for character building, but it's a great place to start your engine when you're stuck at the beginning of that epic novel you're struggling with.
I also find "The Birth Order Book" by Dr. Kevin Leman helpful while developing my character, as well as a post on crafting compelling characters by David Corbett that I LOVE here.
And p.s. I'm curious. What's your Disney Princess/Prince? Why?