There are many steps in the writing and editing process. All of them are important: -plotting, drafting, editing on your own, critique partners, and beta readers. But before you start sending queries, I firmly believe this should be your final step:
Read your manuscript out loud OR put it through a text-to-speech reader.
You may have heard this advice before. Maybe you've done it, maybe not. Maybe you started reading out loud and gave up when you got tired of hearing the sound of your own voice. (Trust me, I've been there.) And the reason for reading out loud might be obvious. You can catch short missed words like "and", "a", "the". You can find out if you've used the word "bookstore" a few too many times within a few paragraphs. And you can locate spots where dialogue is stilted.
Maybe you think you've already caught all those issues after reading your story six times and sending it to a handful of others to read. And it's possible you've caught most of them. But you can never be sure. It's easy for our eyes to skip over a missing word because our clever brains fill in the blanks.
If you read every single word out loud as if you're creating an audiobook, you will find something to fix. Since you're the author, you know how you want your many characters to sound. You know every inflection you've intended to construct. And yes, I know this is extremely time consuming. You're tired of reading your own words again and again. That's why a lot of writers don't do this final step - and I totally understand. But if you skip this step, you're doing yourself a disservice. You obviously want your manuscript to be the very best it can possibly be before you query an agent, editor, or publishing house.
I haven't always done this step in the past, but once I did and realized how many things I could change, I'll never not read my work out loud.
Or have an app read it to me.
You can find a lot of different text-to-speech apps, but my favorite is ttsreader.com. There's a handful of voice options to choose from as well as different reading speeds. (Side note: sometimes I enjoy hearing it read with a UK accent. It can be kinda fun!)
Even though these apps can't express those inflections - and sometimes the voices are downright annoying - it's still as helpful as reading it with your own voice. I like to do it chapter by chapter; I listen while reading along. You have no idea how many times I've stopped the app so I could change a word or add in something I've missed. That's my reasoning for believing in this final step. It works. I know I've made my manuscripts better by doing it, and I know you can do the same.