It occurred to me I haven't written a "craft" kind of post in a while. So, here goes nothing. (No, really.)
Recently, a fellow writer asked my opinion regarding POV (point of view). Her editor told her a sentence in her manuscript changed her POV, but she disagreed. I asked the writer to read me the entire paragraph before the sentence and...yeah. I came down on the editor's side.
How's the best way to explain POV? Pretend you're an actor/actress. The book you're writing is your script. Now immerse yourself in the character who's relating the scene. What does (s)he see, feel, hear, taste, and say? When it comes to POV, dialogue is the least important (though still vital--if your character is an eighteenth century duke, he's clearly not going to utter the phrase, "Surf's up, dudes!")
For argument's sake, let's use the names Linda and Larry. (I'm in an alliteration mood right now. Roll with it.) If we're in Linda's POV, she'll see Larry's expressions, hear what he says, feel her own reactions to what's happening around her. She can only assume what Larry sees, hears, and most importantly, feels. That last one usually gets writers into trouble (including my friend from the opening paragraph.) So if we're in Linda's POV, a sentence like, "Larry couldn't believe his ears" is a no-no. You can write, "Larry's widened eyes and slack jaw suggested he didn't believe her" because that's still in Linda's POV. Linda is assuming Larry's thoughts, based on what she sees. She might be wrong. Maybe Larry's wide-eyed and slack-jawed because there's a tarantula crawling up Linda's shoulder. But unless Linda suddenly feels the furry-legged sensation, turns and notices the black arachnid creeping closer, or hears the words, "Umm, Linda? There's a spider on you" she can only assume the reason behind Larry's expression.
Does that make sense? Or would you like another example? Write and let me know!