Early in the play, conformity is presented as a cultural issue for the Puritans in Salem. The notion of taboo and social transgression are defined, largely, along the lines of lack of conformity to clear and popularly enforced social codes. Additionally, church attendance and even modes of speech are discussed and depicted as issues governed by or related to conformity.
The girls who dance naked in the woods before the opening of the play are subject to quite severe punishment - even death. The crime they commit is that of breaking with the dictates of the church. This is, effectively, the definition of sin in Salem.
Proctor is chastised for exaggerating when speaking to Reverend Parris early in the play. Proctor says that if there were a group of people formed in opposition to Reverend Parris and his church that he (Proctor) would gladly join it. Rebecca Nurse speaks out and attempts to make Proctor recant his statement. His speech does not conform to the standards of religiously defined morality of expression.
Proctor's poor church attendance is also shown as an example of his lack of conformity to an otherwise universally agreed upon social code. Puritans in Salem are expected to attend church without fail. It is the church that keeps them together. In some ways, the church is used as a means to threaten individuals and (seen positively) mold behavior toward acceptable ends.
People do not want to be seen as straying from the church or failing in piety in this society. Conformity to convention is what defines one's true membership in the society. Non-conformity confuses that membership, as seen in the example of Proctor when he confronts Reverend Parris on several occasions.