There is a really great e-book written by Poets & Writers about book promotion (The Poets & Writers Guide to Publicity and Promotion) that is well worth a read. It has chapters on various ways to help promote your work on little-to-no budget. One whole chapter is on book trailers. They talk about using trailers to really introduce the idea of the book, and to help readers get a sense of what the book is about. It really works the same way movie trailers do. I think right now it's more of a fiction thing, but I found a really great trailer on YouTube by Alaskan writer Vivian Faith Prescott (The Hide of My Tongue is her fabulous book of poems). That trailer gave me some good ideas to get started.
I think this one might be a little long, and I'll keep working on it, but here it is. I'd love any feedback!