I have a more difficult time with transitions in my life than most people (sometimes) so I understand why there are those positively CLINGING to traditional publishing. Especially if you were treated well or are still treated well. Like they are polite and pay you. It's hard to see digital as anything but the enemy.
Digital is my friend, right?
There are professionals who cannot see the difference between a digital book cover and a physical cover. They continue to design and approve of approaches or design elements that work in print that cannot hope to work in digital.
Let me restate what should be obvious. The text should be readable on the cover. The bigger the better. This isn't art, it's a billboard to sell your book.
This isn't art, it's a billboard to sell your book.
So cutesy little phrases that people can't read without using their browser to zoom in don't work. "A Novel of the Edwardian Era" BZZZZT Thanks for playing, see ya again when you recover from being slapped upside the head with a 2x4.
Keep your name relatively the same size as the title or larger.
Subtitles. If the book is part of a series, that information should be on the cover. If it's not you have room to include something like "A Cozy Mystery", "A Contemporary Novel" or some description. This should be smaller. If you're fortunate enough to be award winning you could include that.
BUT you have to be smart since you DO want the image to be seen. Don't include too much text. Don't clutter up this small space.
I'm a lot happier with including the subtitle in the book's description--"Miss Grayson's Gambol: An Edwardian Novel"--than putting that on the cover. The subtitle will appear in the listing and not clutter the image.
These are ideas you should consider whether you design the cover yourself or have someone design one for you.