Double check your paper before submitting it. Use self-detection plagarism sites such as plagiarism.com/self.detect.htm and scanmyessay.com/plagiarism-test.php to check work before submission to eliminate the possibility of accidental plagiarism.
Compare writing styles if you are reviewing someone's work. Compare the suspected plagiarized paper against another paper that the person has written. This can be an indicator of plagiarism. If the author is using different tone or voice, this may indicate that the work was plagiarized.
Check for a wider vocabulary range and unnoticed spelling errors. If the person writing suddenly has a very wide vocabulary, it can indicate plagiarism. Certain words that may have made it through spell check may also be an indicator. These are words such as "colour" as opposed to "color," and other British-English words that the person may not have noticed.
Google suspicious text. Google is the No. 1 search engine in the United States, making it one of the first places people go for research. Plugging suspicious sentences into the popular search engine may result in a quick answer to the plagiarism question.
Utilize plagiarism sites. There are several websites that carry databases of papers that will scan the text against other written documents. These databases are sometimes paid for and supported by universities. Some plagiarism checker sites are: turinitin.com, ithenticate.com, plagiarismdetect.com, plagiarismchecker.com, and dustball.com/cs/plagiarism.checker.