There's a rumor going around, and like most rumors, it has basis in truth, but as stated, is entirely wrong. What's the rumor? "Book trailers are just movie trailers, but for books." Sure, there are lots of similarities, but that's a bit like saying that a house cat is a kind of lion. While true technically, it focuses attention on the wrong elements, leading the listener to essentially un-true assumptions and interpretations.
See, there's one huge and very important difference between a movie trailer and a book trailer. One is for movies and the other is for books - or more correctly, one is for movie people and the other is for book people. And one of the big differences between those two types of people, in my estimation, is that movie people watch trailers because they want to see what a movie looks like, while book people watch trailers because they want to find out what a book feels like. Feels like, not looks like.
Let's face it. Most book people read books - at least, in part - because they enjoy the process of filling in the visuals for themselves. That's why many of us hate to see a movie based on a book before we've read it. Doing so robs us forever of that joy of imagining the world for ourselves, because once you've seen the movie, it's pretty hard to set those memories aside and imagine things from scratch.
If that's true, then the last thing a book trailer wants to do is to depict the actual settings and characters of the story, thus ruining things for the reader. And whatever you do, don't try to dramatize actual events from the book. That's even worse.
So what's an author/director to do?
The best answer I've been able to come up with is that we try instead to convey the mood of the book, with only a vague and non-specific adherence to the facts, details and events. For example, if your book is a boy-meets-girl story, maybe your trailer should show five or six scenes of typical boy-meets-girl activities, but with different actors in each one - a sort of montage or pastiche of the events of the book, conveying the mood without overly depicting the details.
That's the approach I'm taking in the trailers for my first book, Strange Places. For the first trailer, no characters of any kind actually appear on screen, yet it's tearing up the YouTube charts. It's too early to say how successful this philosophy is going to be, but the reaction I'm getting so far is that readers are liking this approach. And based on that, I've got a second trailer coming next week that I think is going to blow you away. Stay tuned.