I've seen some horrific attempts at creating a book over there years. Since InDesigns creation, it's only become worse. The above was sent to me by a regular client,(yes it's really small so you can see who did this) and when I converted his PDF back to word, I found out just how deep the problem went.
The manuscript had been sent to a friend of his, who offered to do the work for free--because let's face it, publishing is a hard gig.
So at first glance I expect everyone to notice the oversized margins. Yes, whatever you send to a printer is the way the book will print. so that small text and large amounts of white space would be disasterous.
Now let's talk consistance. The headers should match. Either by being on the outside of the page or the center of the page. Alternating. If on your print ready document your title, author, and/or page number are not on the correct outside margin, then you will lose the text into the center of the book, where it does no one any good. Example, those page numbers at the bottom. One of them is gone to the gutter of your book.
Now, what you can't see, InDesign made a mockery of this manuscript. Extra Section breaks, which can cause even more issues with your page numbers. Those spaces between paragraphs, while industrially accepted, should never be the same as your text. Smaller (I suggest half of your text) or not at all. I personally hate that extra space, it makes keeping those hanging one word, or short sentences, from happening next to impossible.
Just a few basics to keep your book looking it's best.