I don't ever send anything out without getting other eyes on it. This is because they ALWAYS find something. Your (or "my" anyway) vision is limited, what you write is an interplay of what's in your mind and what goes on the page. Someone else just gets the page, they notice the gaps that your mind filled in for you. We're often not as clear as we think we're being.
In my experience, they don't even have to be writers. Some people just have a knack for it. We're all readers, and they know if something sounds clunky, isn't believable, bores them, or whatever. It ain't rocket science, right? (I wouldn't wait for the gatekeepers, btw. They're most likely to just reject it if it's not polished, in my experience).
I used to put everything up for critiques and get several opinions. Then I'd re-write, repost for another round of critiques, and make any final changes before sending it out.
After a few years of that, I realized I wasn't getting much out of it any more for the ton of time it takes to return all the favors. I've heard other writers say that too, that after a couple/few years and lots of critiques (giving and receiving), they don't feel like they need as much anymore. I think there are a few dozen common problems that once you get straight, your writing is much cleaner the first time around.
Now, my husband is usually my only critiquer. It's not the typical "aw, that's nice, hon" thing, though. He's really mean, lol.
So, I write it, he reads it out loud to me and we make corrections together as we go. Then I send it out.
However, every damn time I read a story over I find something else, I just can't help tweaking it. And then if it gets no takers after it's been to maybe a dozen places, I might try shortening it. For some reason, I've had great luck with cutting stories way down, even when they seemed tight to me to begin with. ?
Anyway, it's only finished for sure after someone accepts it. Then I seem to lose all interest in it and may not even read it when it comes out.
That's my method, anyway.