What is author intrusion? Anything that pulls you out of the story and makes you remember that a person wrote the words you're reading. There are several ways this can happen, but there's one that's common in self published novels.
Meaning, the author doesn't trust the reader to make the connections and keeps beating them over the head with:
"Pay attention because this is important."
"Let me tell you in case you didn't understand what I just showed you in that last scene."
Have you ever done that? I wish I could find some of my early writing to show you what I mean. It was bad. I'd write a lovely showy bit and then ruin it by explaining what I'd just shown though action or good dialogue. Luckily, now that I've noticed it in other books, I'm getting better at cleaning up my own manuscripts.
We must remember that our readers are intelligent people. They're readers for crying out loud! I don't want someone to treat me like I'm stupid, and neither do my readers.
Here are two other things I've seen that can be avoided. All of them fall under author intrusion because they can jolt me out of the story and remind me that I'm reading instead of living vicariously through the characters.
1. Distant POV (I'm guilty here in my first drafts!) I want to see and feel right along with the hero. This means getting deep in their head, even in third person. When the writing is like a fly on the wall it's hard to really care. Make me laugh, make me cry, make me sit on the edge of the couch.
Here's a great review of the different kinds of POV.
2. Dropping in a phrase, technology, something that just doesn't fit the world. This happens in historical fiction sometimes. Modern slang or a reference to something that the character shouldn't know anything about. This could include something the reader knows from a different character that the main character shouldn't know about.
Do your research and then comb through to make sure everything is accurate for the world or time period, as well as double checking your own facts and timeline.
1. Spend more time on your novel. Don't write it and then hit distribute on Createspace. Let it sit, revise, let someone read it and listen to what they say. Revise it again! Get the picture. Self publishing is faster than traditional, but good publishing still takes time.
2. When you think it's ready to share with the world, hire an editor. I can guarantee they will be able to help you make it better.
Close vs. Distant POV by Annette Lyon
A POV Footnote on SFWA (cause you know I love scifi) This talks about a lot of other things, POV drift, saying something a real person would say, show don't tell and have sufficient motivation.
POV chart is from another great blog post--Who's story is this anyway?