Regrettably, Abigail can be considered the main catalyst to the drama in Miller's work. I think that you can find more than three actions that impact the story in a significant way. For me, I think that some of the most telling moments come in the very first Act, the very first scene. Consider how Abigail acts towards the girls when the adults are gone. She is the ringleader, the driving focus behind the rumors and the entire situation surrounding the accusations of witchcraft in Salem. When the other girls reflect a moment of weakness in wanting to "come clean," Abigail demonstrates herself to be "the straw that stirs the drink:"
Abigail, however, asserts herself as the strongest of the girls, bullying the others into admitting nothing other than the fact that they were dancing in the woods.
Another significant action that Abigail takes would come in the very next scene between her and John Proctor. When both of them talk, Abigail reveals the fraudulent nature of the witchcraft charges and it becomes quite evident that she wants John, willing to do anything to rekindle the spark between them. I would actually jump to the end of the play for another action of Abigail that is quite significant. When it is found that she has left Salem, robbing Parris of all his money, it reflects Abigail's character to have started the calamity in Salem and abandon the town in the wake of what she created. I think that her departure reflects much of her character and also displays that no matter what, Abigail, as well the townspeople of Salem, will not face a happy ending in their capitulation to fear, suspicion, and abdication of collective solidarity.