As you develop the habit of revisiting your highlights, you'll increasingly start to think in terms of your future self. As you highlight, for example, you might starting asking: Will my future self be able to understand what this passage is saying and why I highlighted it? To ensure your future self has enough context, you might then also take much longer highlights.
To become a more proficient active reader who uses highlighting effectively you need to think about what contextual information will be required for comprehension when you review annotations in the future. Longer highlights may be required.
<small>Detail, London, British Library, Harley MS 3487 (13th century)—[source](