This semester has been an education in plagiarism. As a student, it is important to be aware of how plagiarism is defined. It is one pothole that is easy to fall into even if you are trying your best to avoid it. The old saw that you cannot be called on for plagiarism if you sight your material is not correct. The rule that I was told was that if your work contained more than 30% material that was similar, wither it was cited or not, is considered plagiarized.  Two or more sentences was  major plagiarism. A big shock to me was recycling your own work with citing is considered plagiarism.
My advice, as a student: subscribe to a plagiarism checker.  This post is considered 5% unoriginal by mechanical means.