The term promotion means different things to different people, but the simple understanding is doing whatever it takes to get your book the attention it deserves!
A good trailer is about atmosphere and a glimpse into your story. There are three elements needed: visuals, soundtrack, and a story.
Remember, the more you include the more interest your audience will have in checking out your tour appearance. And it will be more fun than sitting at a table waiting and hoping for someone to stop by and purchase your book. (One of the drawbacks of traditional book tours is you may sit for hours and none or few people stop by. It can be a real downer. But a virtual tour is not that way.)