How are reading strategies for subject content different from reading strategies for fiction?

Reading Subject contents is intended to learn / acquire new information.

Reading fiction is intended for entertainment.

When designing strategies to learn, you need higher level of focus and adjust it to your learning capabilities. You will need to put more effort to understand the content of the book.

This will be a lot of different compared to designing strategies to consume entertainment. You can do it however you feel comfortable. The stakes is significantly low compared to reading to acquire knowledge.