Stories are usually character-driven...making your characters the most important part of your novel. The more interesting and believable your characters, the better your book will be.
Great characters can make up for a so-so plot. Look at the Marvel films. Most have the same basic, well-worn plot (evil threatens the world, heroes must work together to save it), yet the characters - the deeply flawed Tony Stark, fish-out-of-water Thor, brooding and back-stabbing Loki - keep you coming back for more.
We love these characters.
The same goes with your books. If you have characters people love, readers will buy your books just to see what they do next. So how do you create characters for your book?
Do you create an excel spreadsheet, writing down every detail of their past, their psychological profile, their favorite colors, their strengths and weaknesses? Do you draw detailed pictures of every item of clothing they own? Every relationship they've had? Their hopes and dreams?
I would caution against it.
Now, of course everyone has a different way of writing, and of creating their characters. But in my experience, the more detail you use when initially creating your characters, the less real they become.
Because, in over-using your logical brain - the logical, list-making, problem-solving part - you stifle your creative brain. That part that seems to work by magic, creating things out of thin air, without you having a damn clue how you did it.
Now, as a physician, I can tell you that I have a well-developed logical brain. I'm all about facts and math and problem-solving. But as a writer, I have to turn this part of my brain off. I've never fully created a world, or a character, with this part of my mind. Sure, you have to start with it. Maybe you outline the basics: the rogue with a heart of gold, the bumbling mad scientist, the wise wizard, the rich, dominating businessman - but when it comes to writing the character, turn that logical brain off.
See, your characters - after a certain point - should write themselves.
You'll be in control at first. You'll use your logic-brain to write them...until they start being real to you. Until they come alive.
Once that happens, your creative brain takes over. The characters start writing themselves. They tell you what to write. When you try to force them to do things they wouldn't do, they resist. They push back. You start to feel like your writing is going in the wrong direction. You start to get "writer's block."
And if you try to force them too much, your readers won't believe in these characters.
You see, your logical brain just draws the barest outline of a character. Just enough that you can kinda tell who he or she is. Your creative brain fills in the details, the colors. It animates that character. Breathes life into them.
Now, sometimes it takes a long time for a character to come to life. I've written 90% of a book feeling like one or two of the characters is still dead. A wooden, lifeless stand-in. So I re-write these characters. I do it until the character comes to life. And when they do, I sometimes have to completely change their whole side of the story. Because they tell me what I need to do. This happened to me with Erasmus in the Runic series. And with Sukri and Gammon in Hunter of Legends.
I can tell you, with utter seriousness, that after the first novel in a series, I write for the same reasons a reader wants to read...to see what happens next. To see what my characters will do.
Because I have no idea what they'll tell me to do next.
Because they're alive to me.
I know that if I don't feel this way about my characters - or at least most of them - I'm not doing it right.
So I recommend resisting the urge to over-create your characters at the beginning. Give them room to grow. Leave them mostly a mystery, one that you can unravel over time. Because your readers will be doing the same.