There's no one answer to this question - it depends on the book, the audience, and your own creative vision. However, here are a few tips to get you started:
Start with the cover. This is usually the most eye-catching part of the book, and will give viewers a sense of what the book is about.
Use music and sound effects judiciously. Too much noise can be overwhelming, but a few well-chosen sounds can add a lot of atmosphere.
Use visuals to tell the story. If the book has illustrations, these can be a great way to give viewers a sense of the book's world. If not, consider using other types of visuals (photos, video, etc.) to create a mood or tell the story.
Keep it short. A book trailer should be just a minute or two long - any longer, and viewers are likely to get bored.
Make it engaging. A book trailer should be visually appealing and make viewers want to learn more about the book.
For more tips, check out this article:
https://www.theshelftalker.com/2017/01/how-to-make-a-book-trailer-for-a-childrens-book/