I always kept a couple of pens in different colors, or a hi-liter, so I could mark my notes when I wrote something really important. I also had small sticky tabs that could be placed in the book and removed later if necessary. This was especially true if I was preparing for an open book exam where I would need to find information quickly. Use headings, bullet points, and underlining. Do not try to write too much. If you find you are copying whole sentences, the notes will be very little help to you.