Here is a collection of brief definitions for types of blog posts.
Excerpts - Whether chosen by the author or the blogger, excerpts should contain a glimpse of the story that teases the reader. You want them interested without giving too much away. Generally, they should be no longer than 500+/- words. Anything longer and you are pulling away from your blog.
Promos - These tend to be treated as fall backs for people that either have a busy schedule or aren't comfortable with a more in depth post. They have an important role, and should not be passed by. A well-constructed promo blog is like a billboard – something that catches the interest of the passer-by and gives them just enough information to leave them wanting more.
Character Interview - This is where the blogger assembles 5-7 questions directed at one or more of the characters in the book. Treat the characters as real people and you may get some juicy insight into some secrets the story itself doesn't tell you. Character interviews also help make connections between readers and the book. This is a powerful tool in marketing and promoting.
Dream Cast - This is a great, fun way to show your impression of the characters. By picking a dream cast, you bring to life the story and make invite others to visualize them with you. By inviting comments and opinions on your choices you can encourage interaction with your readers. Interaction is a big ingredient to building your followers.
Soundtrack - Soundtracks are one of my favorite elements. Music travels with people. By assigning songs to various parts of the story line, you can draw in readers that can relate to and/or like the music to discover how it relates to the book. Once they read it, they can then mentally connect the song to the story. When they hear the songs in their daily life it could influence them to share the great story that it reminds them of. As examples: “the Shrek song” aka Rock Star by Smashmouth; “Footloose”; “Kissed by a Rose” by Seal in the first Batman; “Enchanted Melody” by the Everley Brothers in Ghost; “Everything at Once” by Inka in Disney commercials, “Suicide is Painless” for M.A.S.H. … The list goes on.
This or That – I’m thinking this is a mixture of some sort – combining bits of some of the other posts into one.
Guest Post - As the host, you still have the control over what goes on your blog. With a guest post it can take some of the pressure off. The author provides a short article, usually something related to their tour. This can be anything from tips and tricks, behind the scenes, bonus features, back-story, author bio, the motivation behind the story, or countless other possibilities.
Author Interviews - Many people have standard form interviews. While these make it easier for the larger, more established bloggers, I don’t believe it is the best choice for the small blog. Of course there are some standard questions that most people want to know, but if you read just the author’s bio and the summary of their book(s) you can usually come up with a few questions that are more personalized. You only need 5-7 total questions if you add in little tidbits of information and links. If you can’t personalize 2-3 questions then why are you doing an interview?