Social occasions, such as weddings, balls, and parties demonstrate how the characters and their society value class distinctions, wealth, and the strict rules of social decorum.
We see the importance of class being alluded to as Elizabeth's marriage to Darcy grows closer. The narrator shows Darcy becoming accustomed to Elizabeth's working-class relations. The narrator also mentions that while Darcy grew to like Mr. and Mrs. Gardiner, he would always think of Mrs. Philips as vulgar, and that is because, like her sister, Mrs. Bennet, she does act without decorum, and is a shameless gossip (Ch. 18, Vol. 3).
We see that the characters value wealth through several interactions at a few parties. For instance, when Mr. Collins accompanies the Bennets for dinner and cards at the Philipses, Mr. Collins is struck by the size of their apartment and their furniture. He comments that he almost feels like he is in the "small summer breakfast parlour at Rosings" (Ch. 16, Vol.1). He means it as a compliment because Rosings is very grand. The fact that he dwells on Rosings so much as to compare his surroundings to it, shows just how much he values wealth.
We also see just how much the characters value rules of social conduct, or decorum through social gatherings, especially at the Netherfield ball. Mr. Collins embarrasses his cousins greatly by breaching the rules of decorum. He takes the liberty of introducing himself to Darcy, just because he knows that Darcy is Lady Catherine's nephew. This is a great social faux pas. One never introduced one's self in those days in society; one always asked for an introduction. Seeing how disturbed the characters are by breaches of social conduct shows us how much the characters value decorum.