Don't underline too much. The text is likely to be sparse and heavily condensed already. Vary your study note formats. The best way to summarize will vary, depending on the balance of factual and conceptual material. Be flexible and creative.
Idea maps offer unlimited opportunities to visualize technical material.
Look for ways to include them in your notes. Create an over-all picture of the topic. In addition, since technical material tends to build concept upon concept, you need to see how to add newly learned material into the larger context of the topic. Use your study notes for review. Plan regular review time into your study schedule.