Characters, like wild animals, need to be observed in their natural habitat: their story.
When writing a character, a writer should create a situation where the reader can SEE what's happening and decide for himself or herself what is happening.
Show, don't tell -- the mantra most writing teachers tell their students. Here's an example, albeit a simple one:
Saying "John was angry when he read the letter from his wife that ended their marriage." doesn't leave anything to the imagination of the reader, who might see any number of situations defining what "angry" is. Describe behavior instead:
"John fumbled with his key in the deadbolt, pushing the door open with one hand. Tossing his keys on the hall table, not really caring where they fell, he succumbed to an impulse and crumpled the paper he had been reading, propelling the "Dear John" letter down the hall. In the living room, he walked to the fireplace, took down the framed picture of him with his wife, lingering for a moment on her smile, and smashed the teak frame on the marble mantle."
Mind you, it's not Shakespeare, but I think we can all agree that John is definitely angry. We can picture him, holding the letter in one hand as he fumbles with his keys in the other. We can even see his eyes well up a bit as he looks at his wife's image before destroying the frame. It's visual.
Before you write a scene, close your eyes and picture how it looks in your mind. Ask yourself, "How would someone act feeling [insert emotion here]?"
Try it. You'll like it.