Here's how:
hardcopy documents: only use this technique on photocopies, not originals (unless you own the book)
skim through the reading to highlight keywords and ideas: avoid highlighting too much, instead think of your highlighter as a summarizing wand :)
use different colours for different sub-topics or relationships
re-read paying attention to the highlighted text and make point-form notes
use highlighters to reduce your own point-form notes even further
This pdf document is a great resource for understanding how to use highlighting for learning, research, and review.
NOTE: This pdf document is addressed to students who own their textbooks. However, the principles are still the same and to highlight, you could make a photocopy. Also, there are many tools, including Read&Write that allow you to highligh online documents.