I think the trick is just to make sure that every action your character takes is 100% unique to them. When presented with a conflict or situation in which they have to make a decision, what they choose is what they are. Their journey should be them encountering increasingly intense and life-threatening (in a physical or social way) choices, and as the story progresses, their choices hold larger consequences. So under pressure, the choice that your character makes is what reveals their true character. If that makes sense?
For example: Let's say the character's house is burning down. What are they going to do next?? Their choice (being made under extreme pressure) can give the audience an idea of what kind of person they TRULY are.
- if they choose to save their family, they might be presented as a selfless or self-sacrificing character.
- if they choose to run out of the house screaming their head off, they might be presented as cowardly or impulsive
- if they decide to sacrifice their family members in a satanic ritual.. Eh you get the idea.
This is why you should constantly ask yourself "what would MOST people do in this situation? vs. What would MY character do in this situation?"