Read your assignment thoroughly. If your paper has a maximum or a minimum length, this will influence what you can do any given subject justice. Can you write only four pages about the effects of water intake on humans? See if there are any requirements such as peer-reviewed sources, or limitations such as you cannot write on certain topics. Also consider how much time you have to complete the assignment. All of these factors will influence your topic selection, and subsequently your final research product.
Before you even begin researching, consider what interests you. If you don't have an idea already in mind, readings from the course are good places to start to see what piques your interest. Remember, if you want to find out more about something that actually interests you, your research will be much less stressful and much more engaging not only as you write it, but for whoever reads it.
Once you have an idea or two in your mind about what you want to study, do some exploratory research by typing keywords into the catalog, and/or a general search engine. What has already been written on your topic? Who wrote it; are they a reliable source? What has not been written on your topic? How much original research are you expected or willing to do for this assignment? At this point, you don't want to marry yourself to one idea until you have considered the existing literature.
Once you have answered these questions, now you can identify a topic to explore. It is generally easier to narrow your focus if you have a lot of information, in contrast to widening your focus if you don't have enough information.
Now formulate your idea as a question. In this example, we will use "humor as a defense mechanism." If I am interested in exploring this topic, I may phrase this question as "How is humor used as a defense mechanism?"
Be careful not to ask a question, come up with an answer, and try to bridge your question and conclusion. You're very likely to dismiss relevant information this way! This is not what research is; research is objectively answering a question, not picking and choosing evidence to match what you want the result to be.
Breaking down your research question
Now that you have your research question, you're going to break it down again. Ask yourself: what are the major ideas here?
Usually, topics can be broken down by the nouns in the phrase. For this phrase, "humor" and "defense" are the nouns. I chose not to use "mechanism" in this case because "mechanism" is connected with "defense." If our topic was more complicated and had more ideas such as "Humor as a defense mechanism in African-American military veterans under 40," we may need to consider any modifiers: for instance, 40 is a number, not a noun, but is an important part of the overall question.
Major ideas will typically break down into one or two words. Two to four major ideas is ideal.