Episode 1, "Pilot"
-When Chuck sees Jenny at a party, the first thing he asks about her is "is she on Gossip Girl?". This is a hierarchical society - your standing matters.
-In scenes with both Blair and Serena, Serena is always shown alone, but Blair is always framed by allies. This is, of course, how they exercise power - Blair's source of power is social, authoritarian, in numbers, and Serena's source of power is herself, her natural magnetism.
-The episode gives each of the main characters a scene alone with each other, with the exception of Dan/Blair. In those seeds, it establishes common ground and conflict between each pairing, justifying future combinations.
-Jenny and Dan have two different approaches to social climbing - Jenny is just hustling and making the most of every opportunity to get in with the cool kids and she doesn't care who knows it, but Dan is trying to get in through the back door and is very conscious of social climbing while not being seen to be social climbing.