In addition to the initial research you do when selecting and narrowing down your topic, you will likely want to gather resources that provide background on your topic, as well as resources that support your point of view and that help you understand the counterpoints of your argument.
Background research and information lays the groundwork for effective persuasion by providing context, establishing credibility, and anticipating counterarguments. Encyclopedias, dictionaries, and other reference sources are great places to gather background information on your topic.
The most authoritative source on the English language, with a focus on etymology and historical usage.
An online version of the Encyclopedia Britannica
Once you've established the background of your topic for your audience, it's important to start gathering resources that support your points and your argument.