There are several strategies you can follow in order to make sure that your notes do not constitute plagiarism, and one of the easiest ones is to take very short notes. If you only write bullet points that highlight important ideas, but that contain few adjectives or other descriptions, then you will be forced to expand on them when you want to include them in your text. As you incorporate your notes in the text, you will add many words that were not in the original, thus ensuring that the final text is different enough from the original to not be considered plagiarism.