The last thing you want is to go through the whole process of researching and writing your note, only to find out that someone else has written on the same topic. To avoid this, before you begin researching, you need to do a preemption check to make sure that no one else has already written about your chosen topic. This check will help you find any and all articles that have been published or accepted that address any part of your topic, so that you can respond to their arguments, alter your focus or choose a new topic as necessary.
To be sure your topic hasn't been preempted, you'll need to carefully search several databases and review the results. See the "Locating Relevant Articles" box below for a list of the most useful databases. Also, keep in mind that if you're doing interdisciplinary research, journals that cover the other discipline(s) might have relevant articles too.
Preemption checks involve the daunting task of trying to prove the negative. You need to be able to claim confidently that no other article quite like yours exists. You cannot say "there is no article like this" until you have checked everywhere that similar articles might be found, searching every resource that exists for finding law review articles and using different types of searches. So, preemption checking requires an unusual degree of thoroughness and a tolerance for a certain amount of tedium
The payoff for the painstaking work of preemption checking is twofold. First, you can be reassured that you will not spend months researching and writing an article that cannot be published. Second, you'll come away with a portfolio of articles that will help you refine and research your topic.
Once you've gathered a list of articles that might discuss your topic, be sure to at least skim them. You probably don't need to read every article in its entirety, but be sure you read enough to understand what each one is about - it might turn out that while a lot of articles discuss your topic, none of them address the particular aspect that you want to write about.
Suppose you find an article very similar to the one you propose to write. Are you preempted? This is a hard question to answer.
Ask yourself — is there anything at all left to say on this topic? Are their new angles to explore? Can I craft a novel thesis?
Ask an editor or professor. Others may have a more objective view of whether your approach is sufficiently original to merit publication.
Other useful guides (note that many of these guides have links to subscription-only resources):
Preemption Checking for Law Reviews & Journals - USF School of Law
Preemption Guide - UT Austin, Tarlton Law Library
Writing for and Publishing in Law Reviews: Preemption Checking - Gallagher Law Library, University of Washington
If you need help searching any of these databases, please contact a reference librarian.
It is advisable that whenever possible you set up an alert with your topic so you will be notified if anything new is published related to your topic.