How do you guys do it??

I've heard about a lot of writers who are just able to get into a "flow state" when writing. Like, they don't even think about what they're writing, or the grammar of it, or the sentence structure, or if it flows with the entire novel, they just write. I haven't been able to effectively do this since I was 13 or 14 years old (I started writing when I was about 10 years old). My brain is too goddamn loud, and it feels like there's nothing I can do to turn it off.

My problem is this: all I can think about is what's wrong with the current page as I'm working on it. Or, even when I'm considering what's right about it, I'm still being way too analytical and stuck in editing mode, which causes me to write at a snail's pace. Does this paragraph flow? Does it make sense? Is it too repetitive? Should I change something about this? What if it's not interesting enough? It is incredibly frustrating and holds me back on a daily basis.

TL;DR: Please tell me how you guys get your brains to STFU so that you can get into the "flow" of writing, as opposed to trudging through the quicksand of over-thinking and barely being able to scrape together 200 words per day.

^{(P.S. Merry Christmas to all who celebrate!})