Every character needs both internal and external conflicts to be three-dimensional. Flaws in people are what make them fascinating. Go through your writing and study your characters to find out what their flaws are. i.e. their internal conflict. How do they disguise this flaw? i.e. their external conflict.

What you do think young Clint is disguising?
Ask your characters questions as if you’re a close friend. Get them to reveal themselves physically, emotionally, and spiritually. Questions like –
1. How do they get on with their family?
2. If they have any siblings, do they like them?
3. Who is the most important person in their life?
4. Where is the most memorable place for them? Why?
5. What was their most unhappy experience?
6. What would they really like to change about their lives or themselves?
7. What are they prepared to do to initiate such change?
8. What do they think about society, religion, injustice, education, wealth, poverty?
There are many other questions that I’m sure you can think of to reveal what makes each of your characters tick, so keep asking them questions until you know them better than yourself.
Then once you know everything about them, visualise their body language and the way they speak; such details will deepen your understanding of your characters and bring them into vibrant life.
However, be warned – sometimes your characters spring into life with so much vitality that they take over your plot! This happened to me when I was writing my WW 11 novel The Invisible Piper. One of my characters, a lion-hearted eleven-year-old evacuee called Charlie was so insistent about what he was going to do in the story that I had to change the plot for him. An interesting, if disturbing experience of a character writing himself in bigger role.