Use quotations as evidence that you've done the requisite research and therefore are writing from an informed position.
That said, you should not merely include quotations just to show that you read something; you will also need to have a clear purpose for including another writer's commentary and make that purpose clear to readers.
One sound reason to including a quotation is to establish the existence of a phenomenon that you want to discuss in your analysis. So for instance, you may not be able to speak of something as a recent trend unless you can point to an expert whose scholarship confirms that the phenomenon is both recent and a trend.
Another sound reason to supply a direct quotation is to add complexity to your own commentary; indeed, rather than trying to simplify a concept, your goal as a college writer will be to show how complicated the concepts are. If something is simple, after all, we might not need a college education to grapple with it, nor would we really need to write about it to learn or teach another person about it.
After you've thought about why you need to include specific language from your sources, the next step is determining which language out of an entire essay, article, or book would be the most useful in your own work. Once you've decided upon the appropriate amount of text to include, then you'll need to work very carefully to integrate it into your own prose.
Yes, that's right: you should meld quotations into your own prose, smoothly and grammatically, rather than simply ending your own sentence and starting with somebody else's. Your essays should not contain what I sometimes call “floating” or "zombie" quotations—that is, quotations that you drop into your essay unceremoniously without introduction or commentary. Anchor these quotations with your words and grammar to prevent them from appearing extraneous, easily skipped, or apt to float away. (If you prefer the other metaphor: like zombies, we know these quotations used to be alive somewhere in some clean context, but we have no idea where they are coming from, and they have suddenly arrived in what looks like an altered state, and now you've made them your readers' problem instead of a source of knowledge. Don't let the undead visit your writing!) Keep all quoted scholarship or other cited material fresh and healthy by ensuring its flesh stays connected to its original blood source and the blood of the new bodies you're allowing it to visit. JUST TO VISIT. Don't let a zombie eat or corrupt your prose! Clearly I've started to push this one too far--but you get the picture.
Even when you use free-standing quotations––those which grammatically stand on their own (i.e., are complete sentences)—you still need to introduce the passage that you cite. Remember, quotations may be interpreted in a number of ways; you must explain how you are interpreting them for readers (without necessarily saying “I think this quotation means X, Y and Z” explicitly).
Here's the general formula I'd like you to practice using: attributive tag + quotation+ citation + commentary/discussion/analysis.
Here's an example:
In his introduction to the play, Ivo Kamps argues that the Duke in Measure for Measure "functions as a representative of divine justice" (Kamps 11). In Kamps' view, then, Vincentio is not merely a rich magnate in Vienna, but rather, a figure of legal and spiritual authority. By referring to the play's justice as "divine," Kamps asks us to see Vincentio as parallel to God, making moral judgments that not only punish other characters in body, but also speak to the fate of their souls.
Every time you read something in which an author uses quotations from a source, pay close attention to how the writer in question handles quoted material. Poor or misuse of quotations will tell you something about the quality of your source, but you can also learn strategies and new constructions from what you see in strong written work.
In your next assignment, I'll remind you of some of the things I've said here and give you an opportunity to work on this skill at length.