I have a tendency as a storyteller to focus on the story and not the characters. Sometimes this works out fine, because the characters are so clear to me that I don't really have to think about their backstory. It just kind of exists, and influences their behaviors without me analyzing it too much.
Oh to be so easy, right?
Well, that's not the case with my current WIP. The story is there, the action and twists and turns are all coming together quite nicely. And the characterization is there, but it's not always solid. My MC is the victim of the story, carried along by what she needs to do instead of what she would do. As my crit partner put it, "I can clearly see her now, but I can't see her how she was before this story started."
Part of this comes from having too much action without enough quiet moments. Quiet moments allow a reader to get familiar with a character outside of the story. Readers aren't distracted from learning new info or following action, they're just hanging out in a private moment with your character. And as we all know from our shower conversations with ourselves, private moments bring about unguarded actions that reveal us more than anything else.
Sometimes this comes in the form of quirks. Maybe your character talks to himself when he's alone, or sings show tunes, or cries when there's no one around to see him in a moment of weakness. Sometimes it's an action or behavior so ingrained they're not conscious of it, but it speaks volumes to the reader.
For example, the MC in my current WIP is an archer. In one scene, she's stuck between a rock and a hard place (literally) and needs a moment to plan. As she debates her decision, she strokes the fletching on her arrow. This services the scene on two levels: on the most immediate level, we see her nervousness in the habit. And the action speaks more about her nerves and internal prep than me as the author just saying "she was nervous and preparing for the next step."
But on the higher level, the reader sees it as a habit. It's a reminder: she's done this before. She knows to check the fletching for breaks, it's an action ingrained in her since she first learned how to shoot. She's probably done it hundreds of times before, in moments just like these, and suddenly we have an insight into her past. If she's been around arrows enough to pick this up as a nervous habit, then archery must be important to her life. It must have served a large role in her childhood, which naturally leads to more questions. Why? For how long? What else did it influence? And so on.
The moral of the story here is to give your character intimate moments with the reader. When you find those quiet scenes between actions, use them to build up the rapport between your character and your reader. These moments are insight into the MC's true personality, and allow you to share back story through their actions without info dumping on your reader.
How do you like to use your character's personal moments?