I think you have to figure out who your character is-- including what they feel, want, hate, love, think, and so on-- to help them come alive. Also, why they feel, want, hate, love, think and so on about certain things. Give them a situation-- how do they react, why?
What is it that your character wants more than anything else in the whole world? Why? What are they willing to do to get it?
Think of what defines you-- and what defines your character. And why. I think the why is important because it gets beyond the surface level. Ex. Protag hates people. Okay, why? Becuase she's doesn't like insincerity and is afraid of believing in someone's veneer only to find that it's a sham. She has serious issues with trust, clearly. Ah, but why-- because her parents were too wrapped up in themselves when she was young, this led her to be both independent and distrustful. Most of this would NEVER end up in the text, but when you write your character, you can keep them true to themselve (unless you're purposefully changing who they are for their personal growth.)