2. Don't write down too much
Your essay must be an expression of your own thinking, not a patchwork of borrowed ideas. Plan therefore to invest your research time in understanding your sources and integrating them into your own thinking. Your note cards or note sheets will record only ideas that are relevant to your focus on the topic; and they will mostly summarize rather then quote.
* Copy out exact words only when the ideas are memorably phrased or surprisingly expressed -- when you might use them as actual quotations in your essay.
* Otherwise, compress ideas in your own words. Paraphrasing word by word is a waste of time. Choose the most important ideas and write them down as labels or headings. Then fill in with a few sub points that explain or exemplify.
* Don't depend on underlining and highlighting. Find your own words for notes in the margin (or on "stick" notes).