A lot is, of course, dependent on the player. I have one player who I consider notorious for not reading up on anything - rules, handouts, the lot. And this is not because he's dyslexic or anything like that. So the obvious solution is not to give him any handouts longer than two lines, and not having the session depend on him having read what I've sent him before it.
I have a heavy to industrial strength dyslexic player, too, who also needs special consideration. Whenever possible, I make sure he's not the only one with the handout if it's that important, I use short words and sentences if I expect him to get it - and I prefer to take him aside and read it to him.

But you know, most of my players read what they're supposed to read. Three of them even swallow anything I send them eagerly.