As writers, we work very hard on our writing. We make sure our sentences dovetail together, check that the meaning is as clear as possible, and, of course, proof for punctuation, misspellings, or grammar goofs. We read our copy over and over, and then it happens.
Your mind sees what is supposed to be on the copy, but it's not really there.
This happens to most writers. It becomes better with years of writing experience, but still it can happen. However, you can take precautions to guard against it.
Let your work rest . . .
If at all possible, let your freshly written manuscript rest for several days, weeks, or even months, so you're coming to the work cold. This helps your mind reboot and you catch many of your own errors. You'll be amazed what you'll find.
Read out loud . . .
Reading your pages out loud helps give you distance. You may feel silly reading to yourself, but actually it is good because you can more easily feel the rhythm of your words and if the words aren't right you'll notice. Also try reading your work to others. You'll see your work as others do and this awakens your mind to what is really on your copy.
Edit your manuscript backwards while listening to something else . . .
Try line-editing your work while listening to the radio or TV. This gives some writers the distance they need. I have heard of other authors who read from the bottom of the page up and swear this helps them find errors. It drives me nuts, but whatever works is great.
Proof-readers . . .
This is the best way, in my humble opinion, to fight writers blindness. If I'm up against a deadline and can't wait to let my pages rest and after I've read my manuscript many times and even out loud, I will turn it over to trusted proof readers. Proof-readers are cold to your work and can easily catch mistakes. The more eyes reading your pages the better because what one person doesn't see another one will. Just make sure that they know what they're doing and that you trust them.
What about you? Do you struggle catching your errors? What do you do to guard against it?