I'm currently at this phase of the process with The Loudest Meow, and I thought I would share some thoughts with you about this stage in book production:
Make Sure You're Ready: You should move on to proofreading after your book has been thoroughly edited. When you get to this point, you should be thinking about typos and repetitive words and missing words and absent periods. It should be that level of error at this stage.
Get Help: On my first book, I thought I could be my own proofreader. How hard could it be? It turned that I had to learn the same lesson that I learned from beta readers and from editors. At certain points, you have to let go of your book and allow another pair of eyes to review it and report back to you. For whatever reason, you just can't see the mistakes any more. And then when it's your turn to reclaim your book, you read the suggestions, and the errors look as bright as day. How could you have missed them? But you do. You need that outside assistance.
Review and Let It Sit: After you have received the manuscript back from your proofreader and have gone through the suggestions, you need to let the manuscript sit, even if it's just for a day or two.This time, I didn't pick up The Loudest Meow again for five days. This is hard for me to do. Letting it sit feels like I am doing nothing, but I actually am doing something very important for myself. I'm exercising my patience muscle. I'm practicing faith. I am someone who likes to move quickly through life. I'm afraid that, if I slow down, I will never accomplish anything. I have had to reframe “Let It Sit” as an action item that I need to do. I think it's important in order to look at it with fresh eyes again when you return to it for the final time.
Read It Aloud: I just went through this step today, and I was amazed by how much I still caught. I find reading aloud is a great way to find repetitious words and to hear inherent clunkiness. I believe this is a really important step to do.
Spellcheck Again: I didn't want to do it. My prideful voice said, “This is overkill. I caught everything.” I didn't. I'm so glad I followed through.
Smile at the Illusion of Perfection: You do your best. Every time you write a book, you can work on your process to make it more effective. After it's published and you pick up your book, you might see a word that you wish you had changed. Then you have to assess the importance of the error. If you're an indy writer, you can always take your book down and republish, or you can decide that you can live with it. In some ways, proofreading is never done.