All quotations from Shakespeare or other playwrights who use such divisions should list act, scene, and line numbers-and, where appropriate, the speakers of the lines, the scene descriptions and stage directions in the script, etc. After an initial note specifying the edition you are using, you need not use footnotes to do this. For example:
Puck's lines at the end of A Midsummer Night's Dream associate the audience's experience of the play with the lovers' experience in the woods:
If we shadows have offended,
Think but this, and all is mended:
That you have but slumb'red here,
While these visions did appear.
And this weak and idle theme,
No more yielding but a dream. (5.1.409-14)
For plays using only act and scene designations, cite those and the page number of the edition you are using; for one act plays the page number will be enough.