Every character in Friends is different and distinct, with their own foibles and quirks. Monica likes to clean; Chandler fears he's gay; Ross gets divorced; Rachel’s into fashion and shopping; Phoebe's kind of ditsy – and poor Joey's not the brightest bulb. Everything they say and do supports their characterization perfectly.
An episode of Friends usually starts off in the coffee shop. Then, something happens to upset the norm and the characters must fight against it, accept it or adjust to it. By the end of the episode they're back at the coffee shop, equilibrium restored. We're never subjected to the boring bits (sleeping, eating, getting up, etc.); everything we see relates in some way to the plot and is there for a reason. In short, it's everything I need to keep in mind for my own writing. I knew there was a reason I liked it so much!