If you've never seen the movie, it's posted on youtube in its entirety here. It's a great movie and definitely worth seeing if you've never had the chance.
So here's a quick setup that tells you all you need to know for this scene: George (Jimmy Stewart) lives in the small town of Bedford Falls, and his dream is to get out and see the world. But every time he tries to leave, circumstances keep him stuck in the town. He's particularly agitated during this scene, because his brother has just returned to town. George thought that his brother was returning to town to take over some of George's responsibilities so that George could leave town, but George has just learned that his brother has become engaged, and now plans to take a job working for his fiance's father....which will leave George stuck in Bedford Falls, once again.
So right before the scene begins, George, frustrated, goes out for a walk to clear his head and think. He ends up outside of Mary's house, where the scene begins.
Some backstory on Mary: she has always had a crush on George, and the record that she plays (and the artwork she places on the easel in the scene) are references to a night she and George shared years ago. Obviously, she's still thinking about that night and trying to remind George of the time they shared together, but he's distracted by his own gloomy thoughts and not at all in the mood to be romantic.
I don't even know where to begin with this scene, everything works so beautifully. It's so well written and staged and blocked that I hate to even try to explain what's going on, for fear that I won't do it justice....but I'll try, anyway, and although there are a ton of great things happening in the scene, I'll just focus on some major ones. But there's so much to see...take a look and check it out beyond the aspects I'm mentioning.
One of the first things to notice about the scene is that--even though the bulk of the film is told through George Bailey's point of view--this scene is told from Mary's point of view. You're with her (and not him) as she runs down the stairs, puts on the record, and invites him in, and you stay with her (and not him) as he leaves the scene halfway through (only to return a beat later). The big reason that the scene is played this way is very simple: she's driving this scene. The scene only happens because she makes it happen. She calls George into the house and she has a definite goal for what she wants to happen in the scene, so it's easy to track the ups-and-downs of the scene as she struggles to connect with George and tries different ways to rekindle her relationship with him. George has none of those layers to play here. Seeing all of her actions up front as she runs down the stairs, check her hair in the mirror, put the artwork on the easel and start the record all help clarify her state of mind and show her deliberate intentions for what she hopes will happen in the scene.
The scene would work even if you stayed with George and saw it all through his point of view as he comes in the house. But that would be a lot less interesting. George has nothing to play here....he's very flat, emotion-wise. He's just frustrated and agitated. That's not interesting, and it's also not fun to be with him and watch him play those emotions. Mary has so many more layers to play in the scene, as she tries to drop hints about how she feels, and then tries to provoke a reaction out of him, and he just acts as a brick wall to bounce those things off of. So it's much better to be "with her", and that's why so many camera setups favor her, while at the same time minimizing him...
...the angles allow you to see the thinking and processing on her face, while not seeing too much of him, so that you can focus on her and her struggle to communicate with him. Again, he doesn't have much to play: he's just stuck in his own head, and brooding about his own troubles. So it's good to minimize him within each setup; we know where his head is at, and his emotional state isn't changing for the first part of the scene. So the staging gives the focus to Mary, so she has a clear stage to play all of her shifting thoughts and emotions.
The blocking is great throughout the whole scene: the movement of the characters really helps give the scene a progression, delineates the "energy shifts" as the scene moves from one idea to the next, and helps illustrate their emotional states and what they're thinking. The overall blocking beats work great: first they are separated by a wide gulf (her in the window, him in the street) and then the distance between them gets lessened as they stand in the doorway, then inside the door, and then stand in the parlor (or whatever that room is), and then sit down together. These progressions allow them to be closer and closer to each other, and allow for tighter and tighter shots as the scene goes on, and also the scene feels like it is building because they are occupying more and more intimate parts of the house as they move from the front yard to the doorway to the inside of the doorway and finally to the parlor.
I love how the staging on the two-shot has depth at first, as she tries to sincerely connect with George...
...and then, after the Mother interrupts, and the scene gets more comedic, the staging gets flat (because staging with depth always feels more dramatic, while flat staging always feels funnier).
Also, George's reactions are more important in this part of the scene, so unlike the first setup (where Mary was doing all of the acting and it made sense to minimize George so we could focus on her), now George has an equal part in the emoting and reacting and we need to give him some screen space so he can play that out and we can see his expressions clearly.
(And, in reference to my previous post about the "Lone Ranger" poster and two objects being equally weighted, notice how Mary is slightly more centered and higher than George. A neat solution to favor her a little and create a good composition).
Then, more great (and yet, so simple) blocking as George stands up. Him standing up is a great way to show that their small moment of not quite-intimacy has been broken by the mom's interruption, and allows the camera to widen out to a less-intimate range so you can feel the distance growing again between them, and to show his continued agitation and unsettled feeling. As Mary loses patience with George and as she begins to get frustrated with him, she stands up and snaps at him to try and get a reaction out of him (again, the simple act of her standing up is a great energy shift in the scene and it's a simple action that helps accentuate the change in her demeanor). And as she confronts him, his frustration gets the better of him and he walks out of the scene. The ringing of the telephone is a great added agitating element that helps adds more conflict to that moment.
I also love the staging as he crosses angrily in front of her and storms out...it allows you to have him leave the scene and linger on her after he goes, and see on her face that she didn't mean to goad him into leaving. The wide shot helps make her look alone and kind of lost in the space as she clearly feels regret over what has happened.
After he exits the scene, the use of the record to show her mental state is just brilliant. It seems so simple, and yet her smashing the record (which is the song they listened to together so many years ago) tells you so much about how she's been hoping things would go with George, and how upset she is that things have gone so badly with him. And smashing a record is such a violent act...it really adds some real punch to that moment, and shows what the stakes of the scene are: she's very much in love with George, and if she can't re-connect with him, she'll be devastated.
Also, the act of him leaving, and her crossing to the record player is all great blocking because it allows the camera to pull back even wider and get away from the closer, more intimate shots we were seeing when they were sitting together. The wide shots (coming after the closer, more tight two-shots and closeups) tell you that the intimacy and warmth of the scene has been lost, because the closer and tighter the shots, the more intimate a scene feels. The wider the shots are, the more distant and unemotional the scene feels.
The whole idea of his hat and leaving it behind is also a brilliant--yet simple--bit of blocking that allows him to come back into the scene...and creates some great staging as she talks to Sam and we see George, behind her, hearing all of this and the effect it has on him. She can be big and powerful within the composition and he is small and less powerful. It shows how much pull Mary has over him in this moment.
And, of course, the idea behind the phone call with Sam is brilliant, because the two of them are forced to share the receiver and be in close proximity with each other, and while the phone conversation goes on, they become more and more aware of each other and their feelings for each other consume them. A great idea to use the phone call (and the prop of the phone) to help tell the story.
Take a look at how the reference to Mother being on the extension (which seems like just a quick throwaway joke) serves an important staging purpose: it allows you to cut away from a medium two-shot of them talking to a shot of Mother and then back to a closer, more intimate setup seamlessly, and helps give the scene a feeling of building intimacy and connection. And the closer shot is great, because you're close enough to focus on their faces, and all the subtle shifts of expression as their feelings blossom without any distracting background elements. And all that subtle acting wouldn't be as powerful in a wider shot (even the first two shot we began with below).
But obviously if you had begun the phone call with this closer, more intimate shot, it would have felt too close and personal for the beginning of the conversation. So you want to build to a shot that is that powerful and so intimate. Always look for ways to make a scene progress and build; a scene should always go from less intimate to more intimate, or less dramatic to more dramatic, etc. Just like the structure of a film, each scene should rise to a climax within itself. A good writer or story artist knows this and uses all the elements of staging and blocking to help accomplish this.
This scene is such a great example of what every scene in a movie should contain: the viewer should have a clear, solid idea of what each character wants out of the scene, and it should be clear in each moment how each character is trying to go about getting what they want, and how close or far away they are from their goal. I love how, in this scene, the staging and blocking change every time Mary tries a new tactic to connect with George, and also changes as she loses patience with him altogether.
And, above all of these considerations, a scene should always be the most entertaining version of that idea that it can possibly be. The characters should be entertaining and compelling as the beats of their story unfold, and this scene is a great example of how to put great characters in opposition and get an incredible amount of fun and entertainment (as well as emotion) out of them as they struggle to get what they want.