You can also look to conversations that Proctor has with his wife. She represents the power of the community, to some degree, as she is fearful of any public announcement of the affair between John and Abigail for what the news might do to her, to John and to their marriage.
I would suggest that you examine Proctor's dialogue in court and when he is being told to sign the declaration. In both of these places, he is attempting to remove the power the courts have over him and take the power away from Abigail. In the end, he refuses to sign his name because it is the only thing he has left. He maintains his power over who he is.
I would look to conversations he has with Abigail. She has some power over him because of the affair. He knows that he cannot reveal the truth about her without revealing the truth of his infidelity to the whole village.
Also look to conversations he has with Reverend Parris. Parris has power over him because he is the one carrying through and validating the accusations of witchcraft. Because Elizabeth Proctor has been accused of witchcraft, Parris holds her life in his hands, thus giving him power over Proctor.