I think this really varies by subject. If you are reading a math textbook with exercises, you can just read the chapter however you want, and do the exercises.

I think this really varies by subject. If you are reading a math textbook with exercises, you can just read the chapter however you want, and do the exercises. Anything you don't understand, you'll be forced to understand by solving the problems. Similarly, if you're reading a computer science textbook, you really need to be writing code that puts your learning into practice, or solving algorithmic problems that use the subject matter. This advice is better when you're just trying to remember stuff that you read in a textbook, rather than gaining a deeper understanding.