Decide whether the play you are citing is a prose drama or a poetic drama. Many modern dramas are prose dramas, composed in standard dialogue and typically formatted by line in accordance with the speaker's name:
MARY: Thanks for coming, Tom.
TOM: I wouldn't have missed it.
In contrast, classic dramas are typically written in poetic verse, although the speaker's name is still identified. Only drama in verse needs to be cited by act, scene, and line; prose plays are cited by page number, as any book would be.
Locate the selected passage in a written copy of the script. If you are finding a classic drama from a reference, you will usually need to look for the act and scene where the passage occurs, then find the appropriate lines yourself. For example, if you are using a Shakespeare quote, the reference you have may say, Hamlet 2.2, indicating that the lines will be found in Act 2, Scene 2 of the play. Written copies of plays will usually include a sidebar indicating every fifth line; if your copy does not indicate line count, you will have to count the lines yourself, which can be a slow process, depending how far into the play your desired quotation occurs.
Parenthetically cite the act, scene, and line of your quote. (Proper MLA citation also includes a Works Cited page, but this does not need to include individual acts, scenes, and lines, just the play's basic information.) In the play's first sequential mention in your paper, the play name should be indicated; it can be omitted in subsequent citations. Your quotation and parenthetical citation should look like this: "A little more than kin, and less than kind" (Hamlet 1.2.65). The parenthetical citation indicates, in Arabic numerals, the act.scene.line.