The type of notes you take will depend on your purpose, and why and how you wish to use the information. You will need to decide what is important, but the following points are some indicators for note-taking:

always identify the main line of argument and reasoning that runs through the entire article and try to summarise it into a few sentences

identify the author's purposes and assumptions (explicit and implicit)

note down single phrases or sentences which encapsulate key elements or the author's purposes or assumptions

take note of details or facts which appeal to you, such as useful statements, statistics or factual evidence

also note items to follow up, such as a question, an idea that offers further possibilities, a puzzling comment, an unfamiliar word, an explanation you don't understand, or an opinion you question