Typos have been plaguing literate humanity since the dawn of publishing. There's even a web site devoted to them. And it's not only a malady afflicting the output of DIY authors. Professionally published books also suffer from this problem – especially eBooks. And this widespread issue is not escaping the eagle eyes of industry observers, who are openly complaining about the proliferation of often embarrassing mistakes, even in books issued by prominent publishers, which boast all the proper resources, so there's no excuse except sloppiness.
That applies to indie authors, too. Sorry, you're not off the hook! And I admit, I am guilty of mistakes in my own self-published works (which is why I'm glad much of it is being reprinted by small presses, though even then, you really need to pay attention to the editorial process).
The good thing about eBooks from a publisher's POV is that they can be mass-produced and marketed inexpensively. In fact, they're often offered basically for free! But that's also the bad thing, at least from a reader's POV. The demand is so high and the product is so cheap and easy to create, and cheap and easy to download, that many minor but bothersome mistakes are slipping through. If the book is produced by a major or even mid-level press, the blame lies with the editor. But when it comes to self-published work, the onus is totally on the author.
Don't go too easy on the work itself, but don't be too hard on yourself, either. Sometimes readers (especially fans of indie authors) can be very forgiving of technical errors if the story itself is well-written and absorbing, so they're not too distracted by minor mechanical mistakes. The early works of the biggest self-publishing author of our time, Amanda Hockings, were infamous for their many, many glaring typos, but that didn't prevent her from becoming a bestselling sensation, and eventually scoring a contract with a major publishing house.
We shouldn't all presume that kind of vindicating success, though. The few Cinderella stories aside, lazy work makes you look amateurish, and can be deemed insulting to your readers.
The problem with editing one's own work is that you know exactly what it's supposed to say, so things like misspelled words, missing words, reversed words etc. will be automatically “corrected” by your inner eye. You really need help in catching the mistakes that will slip through your mental cracks.
Here are a few simple suggestions:
Just be as vigilante as possible! Um, make that vigilant...
Can you see whats' wrong with this sentence? Are you able to forgive typos in your favorite eBooks? Tell me in the comments!