Nora's behavior pattern in the first act undergoes a couple of transitions. When she first comes on stage, it is obvious that she is extremely gay. It is Christmas Eve, and she has just returned from doing Christmas shopping. After she pays the porter who has helped her carry her tree and packages to her door, including giving him a very large tip, she laughs to herself as she eats one or two macaroons. We soon learn the reason for her high spirits. She and her husband used to struggle financially, but now he has been appointed as manager of the bank and will have a very huge salary. We especially see Nora expressing her glee to her friend Christine. Nora is especially happy because now that Torvald will have a large salary, she will no longer owe Krogstad for the loan she took out. Nora is gay in this act because she sees her life as having been freed of all financial burden, as we see her express to Christine in her line, "...for I am free from care now ... My goodness, it's delightful to think of Christine! Free from care!" (III).
In addition to feeling free of financial burden, Nora soon learns that Torvald is now manager over Krogstad, the lawyer whom she obtained her loan from. She is so amused by the fact that Torvald is now Krogstad's superior that she laughs out loud. She even sees irony in the fact that, while Krogstad used to intimidate her, now she thinks she has nothing to fear. She sees so much irony in her new situation that she proclaims, "I should just love to say--Well, I'm damned!" (I).
However, after Krogstad threatens her with blackmail, her behavior pattern changes. She becomes intimidated once again. Nonetheless, she refuses to remain that way and soon busies herself with decorating the Christmas tree while thinking that Krogstad can't possibly harm her.
In short, Nora's behavior pattern throughout the first act is to be gay, lively, to see her situation as humorous and then to refuse to be intimidated by Krogstad.