I have read scripts from beginning writers that start out with crackerjack characters. I get settled in to read the rest of the story and then…nothing. The characters turn flat and the story turns episodic.
Most often after a brief introduction the characters sit (no action) around a kitchen table/in a café/in a park and tell each other their history. Yawn.
Character action and dialogue comes from intrinsic consistency.
One of the best ways to get to know your main characters is to spend a day being the character. What does he eat? Burgers, veggie stir fry, veal? Where does he eat? In the car, in the dining room, in the kitchen? How does she eat? Dainty nibbles, hungry wolf down, slow pace through several courses?
If possible, wear what your character wears. Go where she goes. Travel—by foot, car, horse—as he travels. Treat people the way she would.
Seek out the type of people your character spends time with.
In other words, do as much as possible to live the character’s life for one day.
You will discover small attributes of the character through your interaction with the world. These attributes are just the color and dimension that add reality to your character as you writer. The small details can become the source of conflict and obstacles that add tension to your story.
The difference between sitting at your desk trying to think of character dimensions and actually attempting to live the character for one day is rich with discovery.
Spend a day each for at least three of the major characters in your story. Don’t forget the day as the antagonist.
The bottom line is your story will become rich with detail. Your characters’ s traits will move the story forward instead of being tagged on in a café scene.