Even though I love the act of reading, I often speed through my books as though my main goal is to finish the book, not exactly to imagine it, or to linger awhile with the characters. I am aware of this habit and I can share some techniques that have worked for me.
First, I understand why I scan my books and read really fast, which helps me realize why it's not ideal anymore. In school, there were always large amounts of homework and I simply did not have enough time to read everything slowly and fully absorb it.
Second, I can be pretty sped up at times. I am just a generally energetic person during the daytime.
(Question for reflection: If you scan books when you read, do you know why you do this?)
Here are the techniques that have worked for me.
1. Take deep breaths. Move around before you sit still. Sit comfortably.
2. Imagine the scene. Sometimes it helps to pause after each detail in order to more fully imagine the entire scene. Don't just stop with visual details, but incorporate smells, sensations, tastes, and sounds as well.
3. If you're alone, reading aloud certain passages can help enliven them for you.
4. Keep in mind your purpose for reading. If you really like the book, moving at a slower pace will allow you to catch more details and gain a clearer understanding of it.