1. If the publisher is going to write the genre on the cover, make sure it’s right. I once saw “futuristic” instead of sci-fi. Really?
2. I realize some authors become so famous, whatever they write will sell. That doesn’t mean the back cover should just be a picture of them and nothing else.
3. I know a lot of research goes into many books, that doesn’t mean explain it all at the end in some “Author’s Notes.” For a few books it does work, but there is a fine line. In most others, it just sounds like you are trying to impress people, or worse, explain why you wrote what you did.
4. The teasers on the back of or inside the cover shouldn’t give spoilers to your plot.
5. Don’t put “A Novel” on the the cover. If people can’t figure out what kind of book it is, I’m not sure they should be reading it.