there are plenty of books around this topic. In short there are a at least 4 ways speed reading that you use for different materials. As the other comment pointed out the 1st thing you have to do is stop vocalizing what you read, then you need to learn vocabulary so you would know all of the words without putting much thought to it.
speed reading can really be a game changer, I used to get bored of books myself, but when I can read faster the experience seem to be way more enjoyable!
I can read pretty quickly (I've never really measured, but it takes me about a minute to read a page, which I guess is around 500 words). Depending on the text, though, there's a lot of slowing down or re-reading. I read Harry Potter pretty quickly, but "Thinking: Fast and Slow" is nowhere near at the same pace.