Make sure that quoted material is integrated into your own prose. The quotation must be coherent and grammatical in its new context. In other words, your sentence — including the quotation — must have a subject and verb. Alter either the quotation or your own prose to make the quotation fit.
If you need to omit, change, or clarify a word in the quotation, use ellipses and square brackets to mark your editorial alterations:
Omitting: Mistress Page suspects that Falstaff “hath a thousand of these letters […] and these are of the second edition” (Shakespeare, Merry Wives 2.1.70-73).
Changing: Mistress Page “warrant[s] that he hath a thousand of these letters, writ with blank space for different names” (Shakespeare, Merry Wives 2.1.70-72).
Clarifying: Mistress Ford asks “How shall I be revenged on him [Falstaff]?” (Shakespeare, Merry Wives 2.1.62-63).
In addition to documenting quotations, it is important to introduce them: e.g., “As X has shown,” “As X has argued,” “X suggests that,” or “X seems to believe that . . . .” These phrases help to indicate your attitude toward your source’s statements, and show that you are not taking them uncritically as facts.
The simplest way to incorporate quotations into your own prose is to introduce them with a colon:
Viola’s comments about Feste show that folly is a kind of wisdom: “This fellow is wise enough to play the fool” (Shakespeare, Twelfth Night 3.1.53).