Do your characters justice and get to know them up close. They don't bite! Or do they?
My husband used to stop me in the middle of my workday story to ask who somebody was.
I'd groan, "Candace. I just said her name."
"No, like who is she to you? She's just a name right now."
Well darn. Can I just get that voice in my head when writing stories too?
See, characters are more than names. They are more than blue eyes, jet black hair, or freckles. Characters have eyes that roll, droop, dart, fixate. They have raven hair about as disheveled from lack of sleep as the actual bird after fighting a cat. Their freckles dance about their cheeks and come alive when they grin.
They are more than an emotion, such as nervous
They have a twitch, shuffle their feet, shift their eyes, stutter, get dizzy, get chills, and dread the embarrassment that comes with heated cheeks.
They have quirks
Harry doesn't like gel toothpaste because he uses the other kind on his zits (kills two birds with one stone).
Marge carries a small stone in her pocket and holds it whenever she feels sick.
I wear makeup to ensure my face turns a lovely shade of pink rather than red.
Shelly scrunches her face every 20 seconds to push up her glasses, and her coworkers want to tear those glasses off her face.
They drive the story forward
Harry can't truly let go and spend excessively until something (hmmm what something?) compels him to try it. What would a night on the town with his wallet open look like?
Marge loses her stone on one of her worst days, right when a foreign army invades her town. What will she do? I bet she won't worry about whether or not her face turns red without makeup.
Shelly can't afford glasses that fit, and she faces devastating poverty. Her coworkers don't know that she begins dealing drugs out of the office and will bring a drug war right to their doorstep.
You may learn about your characters as you go, or you may plan them in advance. In order to keep their actions and reactions consistent with their personality, it's important to document them. But howwwww? I hate documenting, I really do. But it helps, and it can be fun if I get inspired.
There are plenty of apps out there. I use Character Planner. It's a great tool for planning just about every aspect of a character including their background, their weakness, strength, morals, even scene extracts.
Careful of the Mary Sue
How about the Mary Sue quiz? A Mary Sue is too good to be believable or relatable. Try one of the many quizzes out there to see where your character lies on the Mary Sue scale. Adjustments may be in order. Make sure you nip it in the bud early.
Use a template
Many people also use a template for character profiles and simply type them up on a Word doc. You can invent your own or start with another list as a base. I just found this one on writerswrite.com.
Store it in your head
I'm such a visual person that I have to do this by watching and admiring other characters on TV shows. How do the characters drive Breaking Bad forward? Sons of Anarchy? The New Girl? I take mental snapshots of how characters react to situations and store them in my head for later. Often what comes out is a mix of several stored people. Careful not to make a character too close to a TV show character; that would be way too obvious.