Every book cover has a title and usually the author's name. These should be clear at every size from thumbnail up to full sized. But that's not always the case...
The other day I was scrolling down my FB feed, which is always chock full of ads for books, when I saw a romance novel with Raped in the title. At least that's what I thought it said. Since I figured that couldn't be right, cuz rape and romance don't go together, I looked closer. The word was Roped. But the font was so stylized the O looked like a A.
This morning, I saw a title with the first three words so stylized all I could make out was the fourth word, which was in a different font. I think it was a romantic suspense novel, but you couldn't tell that from the cover. It took me a couple minutes to understand what the author was actually going for there.
Unfortunately, authors don't have a couple minutes to grab a reader. If they can't read the title, they're moving on to the next book within a few seconds. Bam. The only reason I stopped to ferret out the real answers is because I'm a writer.
Yeah, I know. There are only so many fonts and we all want our books to stand out as different. We all want to get noticed so readers snag our books instead of the next author's. But we really need to pay attention to what the reader might actually be seeing instead of what we think they ought to be seeing.
(Heh, perhaps I should take my own advice there on some of my actual cover images, but I'm not changing any other covers right now)
Anyway, when you're designing a cover, take a step back. Look at it through someone else's eyes. Or have someone else look at it without telling them what it says. See if they're reading what you wrote. Stuff like that.
And if you ever can't tell what my cover is supposed to say, let me know. Sometimes I trip, too.