Get yourself a 4-color pen, or 4 separate pens, some highlighters, and in your own time (not in class), read the material from several sources - Wikipedia, text

Get yourself a 4-color pen, or 4 separate pens, some highlighters, and in your own time (not in class), read the material from several sources - Wikipedia, text book, your professor's notes, understand the topic, then write your notes in your own words, using diagrams whenever possible. Never copy things verbatim especially if you don't fully understand them. Understand the topic first, then write your notes. If its taking you a long time to understand the topic, or it requires some back-tracking or further reading, do that, then return to the topic. Taking down notes in lectures is often a waste of time because often the lecturer is just reading from his/her notes, which you have access to, however it depends on the Lecturer. Final piece of advice is not to take them down in a text file. Use a pen and paper. I find hand-writing the notes is less distracting and forces me to think about them. However this may not be true for everyone.