HAVE AN OPINION!
Close your eyes and imagine yourself back at our first full table read in May. You'd just gotten your role assignment and a script, and you'd found your name tag and taken your place. In your mind's eye, if you look around that table, you realize you have a distinct and specific relationship with everyone in the room. No,you probably aren't super-close with everyone, maybe even have some quiet resentment for one or two, maybe secretly think someone else is attractive but would never say it, maybe worry that someone else doesn't like you... but you HAVE AN OPINION about everyone in that room.
Too often, young actors get caught up thinking that acting is dispalying emotion. That's not precisely true. Acting is pursuing goals: get this one to open up, get this one to fear me, make that one admire me, trick this one into giving me the key. Every moment on stage you are speaking because you want something from the other characters. Your job as an actor is to figure out (or invent) your action/s for every scene you are in. Yes, sometimes you will have more than one action.
The first time we see Augustus and Agatha, he says a poem and she wraps him in a scarf.
Possible Actions for Augustus: Jump through Agath's hoops as quickly as possible to get it over with. Be the best poem-reciter ever because secretly in love with Agatha and wants to impress her. Pick up the pocket candies that are rolling on the floor without Agatha noticing because no one feeds him.
Possible Actions for Agatha: Prove to a watching Ambrose that she is the best governess and therefore would make a great mother. Get Augustus off the path of dissolution by making sure he takes his studies seriously. Prove to the neglected Augustus that he is worthy of attention.
These are neither perfect examples, nor the only examples. I just took a few seconds and tried to come up with some reasons why the people in this scene do the things they do. It's not differnt from real life: we do stuff to impress people, help people, shame people, change people, enlist people to help us, etc. You'll notice that a lot of these action rely on making things up about the characters that is not in the script. For instance, we never learn anything about Agatha's desire for children. So can an actor decide to play the scene that way? Of course, as long as it doesn't contradict anything in the text.
But how can you come up with Actions if you don't know your opinions of and needs from the other characters? Well, you can't. First do the prep work to make the rest of it possible.
Good theater mimics real life. We wnt to see a complex web of interactions play out on stage because in life we have layered and complex histories with those around us.
Your assingment is to write down the names of every character you are either on stage with or who is mentioned in a scene you are in. Then, using a combination of textual evidence and your own imagination, write a relationship. Do you two go fishing every Saturday? Did you fight as children?
What secrets do you know about these other characters? When you take the time to create a detailed relationship with the other characters, it will help you on stage as other characters are talking. Have you ever wondered "how am I supposed to react to this scene?" Doing this crucial work of building detail into your relationship with your scene partners will help you to always know the answer to that question.
Don't worry about gtting it wrong: you can always make changes once you get into rehearsal!