Whenever I write a new story, I love to let others read it and tell me what they think. Once a book hits the sales, you seldom get feedback on what they thought of it. Word of mouth is important and hearing what they may say can be useful. Test readers, as I call them, is a great way to get that feedback. Having someone say to you that they didn't understand what I meant when I wrote this or that within a page helps me to see the sentence or paragraph as it is interpreted rather than how I wrote it. Sometimes meanings can go different ways and rewriting it to be more clear is warranted. Just keep in mind that you have to have a thick skin when someone criticizes your work. I remember in one of my stories my main character cut himself. While he was looking at it, I had written that it was scabbing up already. I was quickly told be a test reader that his blood would never have congealed that fast. I change it.
A good example of how someone reading your story can make you see things different came from another friend of mine. I gave him my story, Remembrance, after I had just finished writing it. He read it and said, "You know, I would put his first nightmare in at the start of the story rather than him waking up and having the nightmare later." After giving it some thought, I decided it was a idea. I changed the sequence and flowed the story together so that when he first wakes up in the story, it is from having that first nightmare that becomes a clue to the story itself. It really sucks a reader in right from the start. Without that kind of feedback, my story would have gone out differently.
I don't always make changes people recommend. Sometimes I listen to what they say but decide it detracts from what I am writing. Someone may say that it would be cool if this person did this or that person does that, but when I think it over, I decide it only pulls the reader away from the main story without a tie-in later. I see it as a distraction for the reader and let it pass. I never discourage that feedback though. Sometimes another story may come of it. You never know.
I have a great proof reader in my newfound friend Pete. If memory serves me write, I think my sister gave him one of my books to read and he reached out to her to ask if I would be offended if he pointed out some errors in it. We connected and he is now my official proof reader, and a good friend.