If you’re with a big publisher, your critique partner should be your editor. But you don’t have that. So the first lesson is the most difficult: FIND A CRITIQUE PARTNER.
This is not a reader. This is not your friend or family or guy at the bar. This has to be a writer. And besides being a writer, they have to be as good as you are – or close. Not a lot better, because that’s a teacher or mentor. Not a lot worse, they won’t have anything to offer.