(1) Your primary goal as an academic writer is not just to get a low similarity score (or a zero). Instead, you want to learn to engage sources fully and robustly, reporting fairly on their ideas and adding your own synthesis, interpretation, and critique. Disciplines vary in how they expect you to build on and mark your own contribution to previous research, but the Poorvu Center offers a thorough discussion of Using Sources that can help guide your choices.
(2) By itself, the Turnitin similarity score does not tell you very much about how your paper uses sources. Instead, you’ll need to review the specific passages that Turnitin highlights as matching the language of your sources. A high similarity score, for instance, could be caused by Turnitin flagging just the titles of your sources in footnotes or bibliography. Sometimes the software fails to recognize quotations that are properly marked with quotation marks or indenting. Most importantly, academic disciplines vary in how much similarity they permit, and sometimes long phrases are just the conventional way to present certain concepts and don’t constitute plagiarism.
As you review the similarities Turnitin has highlighted, you will need to use your judgment, read models from professional and student authors, and—when uncertain—ask for help from your instructors, TFs, or the Writing Center. Instructors who use Turnitin are also alerted that some similarities are what might be called false positives.
If your Turnitin report highlights passages that are not explained by the examples above, you can get more advice by consulting the Poorvu Center discussion of Categories of Source Misuse.
(3) Even papers with similarity scores of 0 can have problems with source use. The purpose of research is to help students enter a conversation with previous knowledge, but a perfectly cited paper can still be immature or underdeveloped. Students who are new to research writing often drop sources in without synthesis, commentary, or interpretation—substituting the sources’ ideas for their own. Turnitin cannot help you identify these problems, which are better addressed through feedback from your instructor, consultation with someone at the Writing Center, and your own careful review and revision.