Determination. You need to decide that you are going to read and not get distracted. You also need to make sure you like the book. If you don’t like a book it is scientifically proven you will read it slower. Other than that, just read. Your brain and eyes will get better at processing the information.
It has taken a lot of reading on my part, but I read the entire Stormlight series in 2 days, with my daily activities, such as school, chores, and sports, still going on.