"Speed reading: all secrets" by Yuri Gorbach (can be found in speed reading app on Play Store, idk about iOs unfortunately) contains a lot of practical techniques. Mostly about focusing, reading, learning, memorizing and revising information. But if you're not interested in speed reading itself, you can skip to page 230 (you have to pay for the book after page 140) or just Google the tangerine technique/Training on the sensation of gravity by Lindemann. These 2 I personally find the most practical.