I went to the biggest middle school in my city, a monster of a 3-story building with annexes, outside buildings and yes, even an elevator. I went to this from a school housing maybe three classes per grade. The whole school building was one floor, and shaped like a big circle, so no student could possibly get lost. That middle school looked massive to me...until I went to high school for a while. Perspective changes everything, and the same can be said when you're talking about editing. You can't make your books perfect unless you change your editing approach, and change your perspective.
Changing Your Perspective
I've blogged about the logistics of editing before, so you already know how to edit your ebooks. But you're not going to catch all the mistakes (and everybody makes mistakes) unless you change your perspective. What does that mean? It means if you're only reading your book on your computer screen, you're not editing properly.
Change the way you're looking at your words. If you've got an ereader, you can upload your book to the ereader before it's ever published live through any online bookstores. It's easy to do: simply connect your ereader to your computer using the provided data cable. Access the device through the computer (a screen should pop up for you once the ereader is loaded) and open up the folder where your ebooks are stored on the reader (on Kindles, the folder is called Archive Documents or something similar). Drag your ebook file directly from the folder where it's stored into the ereader folder; it'll copy itself automatically, so your book won't actually move from your computer hard drive.
Once the file is on the ereader, you can view it the way your readers are going to be viewing it. And once you've changed your perspective, chances are good that you'll find a lot of mistakes you missed the first time around.
Yes, you should read your book the whole way through more than once. Even if you spend a lot of time editing and re-reading during your writing process, nothing can substitute for a good read-through of your work. When you're editing, you shouldn't just be looking for incorrect grammar mechanics and misspellings. You need to make sure you're not repeating yourself (or similar words and phrases) too often, you need to double-check that the plot is hanging together and you need to make sure that the whole book is smooth and cohesive throughout. When you're re-reading your work on an ereader, keep a notepad handy or use the device itself to make notes when you find mistakes, so you can go back to the manuscript file on your computer and make the necessary changes.
If you make a print version of your book, you should absolutely buy a copy for yourself and read your work again. Things look different when they're viewed differently, so it follows that you'll find new mistakes when you look at your book in different formats. When you can read your book from cover to cover (or screen to screen) without finding a single mistake or something you want to change, then you're done editing.