Tools of Characterization
Actions are what finally clues Captain Wentworth in that Anne is more suited to him than Louisa. Louisa's headstrong recklessness in jumping down the stairs in Lyme contrasts sharply with Anne's managing to keep her head and deal with a bad situation. And when Louisa swiftly forgets Wentworth and falls for Benwick, while Anne lets on that she's been carrying the Wentworth torch for over eight years, the differences between their characters couldn't be more clear.
While Anne is technically an Elliot, she feels more at home with the open-hearted Musgroves than with her own family, who snub and ignore her at every opportunity. While the Musgroves invite her along as a matter of course (the trip to Lyme, the box that Charles gets at the theatre), her own family goes off to Bath without her and then demands her presence at parties (like the Dalrymples') whether she wants to go or not. The difference between how the two families treat Anne contrasts the Elliots' coldness with the Musgroves' warmth, and suggests that kinship is a matter of more than blood.
Social Status/Thoughts and Opinions
Why both those tools of characterization are up there together: in the novel, a character's views on whether social status tells you something about someone's character, tell us something about their character. Huh? Think of it this way: if Heather thinks the cool kids are better than everyone else just because they're cool, that shows that Heather cares more about reputation than about personality. So when Mr. Elliot and Lady Russell are arguing that the Dalrymples are good to know simply because of their social status, and Anne counters that good people to know are those who can actually have a conversation, it tells us that Mr. Elliot and Lady Russell think rank in itself is important, while Anne cares more about who the individual is.