While you should never plagiarize intentionally, it can be surprisingly easy to plagiarize accidentally. There are many resources that can help you avoid costly plagiarism mistakes.
-The University of California at Davis' "Guide to Avoiding Plagiarism and Mastering the Art of Scholarship"
-Plagiarism Avoidance Tools from Purdue's O.W.L. (Online Writing Lab) "Avoiding Plagiarism"
-Northwestern University's tutorial "How to Avoid Plagiarism"