One of the hardest but most important aspects of editing your own work is reading it with fresh eyes. You can (and should!) do this with beta readers or by hiring an editor, but being able to do it yourself is so, so valuable.
But how the heck do you do that? After all, when you're reading your own work, you not only know what's going to happen but also what might happen, what never happened, and what happened once in an old version like seven revisions ago!
You have to get out of your head. You have to read your own work as though it were the first time you've ever seen it. You know nothing that isn't on the page! It's not easy, but here are some tips to make it possible.
TAKE A BREAK. This is probably the most common advice. Step away from what you wrote for a while—days, maybe weeks or even months if you can. When you come back to it, you might have forgotten parts, but more importantly, your brain will have the opportunity to approach it like a new thing. That feeling won't last through the whole novel, but hold on to it as long as you can. Also...
TAKE NOTES. As you read your novel with fresh eyes, write down facts and details—especially things that you know have changed from outline to draft or from revision to revision. But—and this is the most important thing—you cannot write down anything that is not on the page! Write down what you see, not what you think you see.
PRACTICE. Believe it or not, seeing a familiar document from a fresh reader's perspective is a skill you can improve at. How do I know? It's literally my job. The more you do it, the easier it will be to see a manuscript the way a new reader would see it, setting aside all the extra information floating around in your head.
This is a very important skill for writers to learn. Beta readers are amazing, and a good editor is well worth the money, but you are the only person in the world who fully understands your intent and your vision. If you can maintain both readers in your head at once—one who has never read this before and the other who knows what you want it to become—you can do anything.
