This may seem self-evident. But students often choose a subject and that's not the same thing. The "subject" is a broad area of study; the "topic" is a narrow area within the subject that can be treated thoroughly within the limits of the assignment.
Given a 10-page paper, which would likely be the better choice? A paper on the history of the French monarchy, or a study of the Machiavellian political skills of Louis XI, the so-called "Spider King"?
At first glance, the history of the French monarchy might seem a better choice, because there's a lot more information. But let's face it. All you'd be writing would be an encyclopedia article. There's so much information that you'd only be able to say a few things about each king, and those few things would be so general that the paper would be abstract and probably dry as dust. Not much chance at all for an original contribution or for having some creative fun.
Entire books have been written on the history of the French monarchy. In fact, books have even been written on Louis XI. Depending upon how much information you find, you might want to narrow your topic even further (thus the narrowed focus I've suggested above on Louis's Machiavellian political skills) so that you leave yourself room to do some original thinking.
Just a point of reference: when it came time for me to write a master's thesis, I narrowed from subject to topic in this way: 19th --century American Transcendentalism (the subject I was interested in). . . Transcendentalist writers in Concord, Massachusetts . . . Henry David Thoreau . . . Walden . . . Eastern influences on Walden. . .Confucianism and Walden. . . Thoreau's use of the Confucian Four Books in Walden: my topic. The resulting paper, which discussed a small handful of Confucian quotations that appear in Walden, turned out to be to be 75 pages long.
Needless to say, if you're going to spend the time it takes to write and revise a 75-page paper--or even a ten-pager--it should be a topic that you're passionate about. Deep interest is the fuel that sends the pen scudding across the paper or the fingers across the keyboard.
Establish a working hypothesis that can guide your search for information. A hypothesis is a prediction of what your thesis will ultimately be. It may happen, of course, that what you find in the course of your research will cause you to change your hypothesis, resulting in a different thesis than what you may have expected originally.
Your level of consciousness determines your world.
Your research project can be a labor of love or a labor of pain. Why have it be the latter? There's too much stress in life to begin with; it's corrosive and the mother of all diseases.
Why suffer needlessly? You have the opportunity here to experience yourself at the height of your gifts. One of the best reasons for your being here at college is that you are committed to inquiry and to the heightening of your intellect. The research project is a microcosm of college education: first is the quest for data and knowledge, then the evaluating of their relevance and validity, then the fashioning of one's individual conclusions with an eye toward advancing human knowledge and making the world a better place.
Do good work and feel good about yourself in the doing!
If nothing else, you need to give yourself time to let your ideas brew.
Beyond that, however, the research paper involves so many different kinds of tasks, each with its own criteria for excellent performance, that it just plain makes sense to spread them out.
The main things are to begin early and to set up a working schedule that allows you to enjoy your work.