As a former Stoic, I condition myself to habit. I force myself into a timed condition response, reinforcing it. My brain does give out, if I focus too much on narrative reading I'll cycle as needed to a ES function like talking (which I am doing now). I hand copy books in whole, if I notice my script is going wonky or I am no longer grasping the text and am just powering through with it without comprehension, I will stop and reread it, and relax my mind and daydream a bit.
Sometimes this is all overwhelming or undesirable so I will turn peripatetic and go for a walk to let my mind roam free.
I also listen to instrumental music at 420 hz. Usually something like cello, contrabass, duduk- no voices or words.
And whatever you do, do not surround yourself with knick-knacks, stuffed animals and pottery in a she-shed in the backyard with scented candles burning and a wicker bowl of yarn by your side as Maia Angelou audiobook is narrated on the speaker while you sip a expresso. This is counter productive and will not help you on your journey to becoming a better reader.