http://ww2.valdosta.edu/~cbarnbau/personal/teaching_MISC/plagiarism.htm
My thoughts on this topic is that, depending on the threshold, everyone plagiarizes. It is something impossible to avoid. There is only a finite way of explaining something in a concise way. A good way to avoid it is explaining two points from different citation sources and then comparing the two, or complementing, with your own thoughts.