I would consider whether you really want to. I'm someone who seems to have naturally not sub-vocalized for most of my life or at least if I did it was like a robotic voice fast talking in my head, I guess I would actually sound the words in my head but much faster than a person talking and in a way that did not help me develop a feel for inflection, etc. I have always been able to read faster than an average person but the last couple years has opened my eyes to a lot of communication issues I have had, basically my default has been that when I talked to people it would always seem very low energy and without much emotion or inflection and it has had a very negative impact on my social life, among other things. In the last couple years I've started learning a second language, in which I find it much easier to read if I do sub-vocalize at a normal human pace and I've also started pushing myself to record myself talking about various topics in English and to work on my communication skills overall. I've now started sub-vocalizing when I read in English as well and I'm noticing overall improvements in my life like being able to have more expressive and natural conversations with people. I'm sure reading without it has its places when you really need to speed read but I'm not sure a goal of never sub vocalizing is ideal.