This is another easy one. One of my clients does this pretty religiously. Do a search in your manuscript document for every instance of two spaces back to back. Just search for space space. Back in the day, in typing classes, folks were taught to use two spaces between sentences. But this is not the standard anymore. It takes up a phenomenal amount of space. It could add two or three pages to your book, just for extra spaces that don’t add to the value of your book. It’s a little thing. But it will save you time, and make your manuscript look better.