If you do not already possess extensive background knowledge of your topic you will need to acquire this information before you begin research on the specific topic of your paper.
Background knowledge can be obtained via resources that provide a broad and high-level discussion of the topic area, such as treatises and casebooks, or similar non-legal academic materials. Books, by their nature, will provide a more general discussion of a topic, compared to articles. You will often find these resources via your preemption check.
This step is also necessary to identify weaknesses in your topic - perhaps the specific issue of your paper has existing, adequate discussion, or the issue is no longer germane. In this scenario you will need to rework your topic. This doesn't necessarily require you to scrap the entire topic; rather, you will use the information you've gained through your preemption check and preliminary research to identify a related, but sufficiently different, topic.
You will need to use multiple databases and Georgetown's library catalog to do comprehensive preliminary research.