I admit, I'm old enough to find the idea of book trailers...odd. The highly professional ones cast actors as the characters, which in my mind is a big no-no. The whole point of a book being better than a movie is that the reader is free to imagine the characters as they will--even as themselves! But it's not my book and it certainly isn't my money. Whatever works, but I think even if I had a million dollar contract with a Big Five publisher, I'd protest using actors. Ask me again, if I ever get that contract!
Book trailers on YouTube seem to fall primarily into three categories, those flashy professional ones mentioned above, Wattpad book trailers filled with stolen video and music (because only a Wattpad writer's creative output is worth copyright protection; nay, their very ideas are pure gold one mustn't steal! But someone else's music or video? No problem!), and Windows Movie Maker slide shows made by indie/self-pub authors with no money.
Why am I blabbering on about book trailers? I made one--naturally. And although I watched far too many book trailers before making my attempt, I'm sure I still left out things that ought to be included. And I am presently doubting book trailers will ever be a service I offer indie authors. There is a learning curve. I slipped many times.
I am accepting all tips from other WMM users, and critique from everyone--I'm a writer, my ego is already calloused!
Now, if I could remember what I'm supposed to do with the trailer, now that it's done....