Tools of Characterization
Characterization in Harry Potter and the Deathly Hallows, Part 1
Actions
We're going to use our friend Ron Weasley as the case study for how actions tell us about character in HP7.1.
Now, we already know Ron is a good guy from previous films, but his actions in this particular installment clue us into some of his less desirable qualities—and his better ones, too (not to worry; Ron's still awesome).
The bad news: Ron seems a little more susceptible to jealously and anger than, say, Harry or Hermione, which means that when he has to wear one of Voldemort's Horcruxes to protect it until it can be destroyed, he gets ridiculously irritable. Horcrux-wearing would definitely worsen anyone's mood (we assume), but in Ron's case, it brings him to the boiling point with his closest friends.
As a result, he abandons both Harry and Hermione in frustration.
HARRY: What's wrong?
RON: Wrong? Nothing's wrong. Not according to you, anyway.
HARRY: Look, if you've got something to say, don't be shy. Spit it out.
RON: All right, I'll spit it out. But don't expect me to be grateful just because now there's another damn thing we've got to find.
HARRY: I thought you knew what you signed up for.
RON: Yeah. I thought I did, too.
Sure, Ron eventually finds his way back and makes amends, but the point is that he's a bit more prone to those kinds of emotions/behaviors than others might be. Good thing he has such understanding friends.
Direct Characterization
This film's characters do not shy away from telling us what they think of each other. Case in point: Hermione. We can see she's super brilliant and amazing, but just in case that truth was somehow lost on the less brilliant among us, Ron makes sure we know:
RON: […] We wouldn't last two days without her. Don't tell her I said that.
Ron has been known to resent how much cleverer Hermione is than, well, everyone, but in this movie, he's definitely embracing it. When Hermione reveals that she has a magical emergency bag with her when they have to leave Fleur and Bill's wedding in a hurry, he's super quick with the compliment:
RON: You're amazing, you are.
HERMIONE: Always the tone of surprise.
Aw, doesn't it just give you the warm and fuzzies?
Speech and Dialogue
Then, of course, characters sometimes accidentally tell us more about themselves when they're trying to talk about other people.
Exhibit A: Voldemort, when he tells his fellow evildoers about Charity Burbage's teaching history. Burbage had been a Muggle Studies professor prior to falling into Voldemort's clutches, and Voldemort finds that totally disgusting, since he thinks Muggles are disgusting:
VOLDEMORT: To those of you who do not know, we are joined tonight by Miss Charity Burbage, who, until recently, taught at Hogwarts School of Witchcraft and Wizardry. Her specialty was Muggle Studies. It is Miss Burbage's belief that Muggles are not so different from us. She would, given her way, have us mate with them. To her, the mixture of magical and Muggle blood is not an abomination, but something to be encouraged.
Since we, as Muggles, know that Muggles are largely awesome, this little tidbit of dialogue shows us just how loony Voldemort is. He's killing a witch because she finds studying non-wizards interesting.
She's not even a Muggle herself (not that that would make killing her right, of course). That whole situation shows just what a hate-driven dude he is.