1-If any characters are visible their faces are hidden. You want to leave the character’s face to the imagination of the reader. This is not always the case. As you can see above some characters are from behind or their faces are cut, but some are visible. I prefer hidden faces, it’s more intriguing ;)
2-The title and image have to be legible in a thumbnail size!
Do your research. Go to the library or a bookstore and look at your genre.What are the common features between bestselling books? For example YA books are colorful, and typically use many fonts
Some great covers of books I did not read and I have never heard of:
Here is what I did with mine:
How long does it take to design a cover? For me it took over a year because I had no idea what I was doing. But keep in mind that now that I have the format all the other covers in the series will be a breeze.
What programs did I use to design the cover? I used Adobe photoshop, which is really expensive, but I had for work. A free, simplified version of Photoshop is available online. Other (expensive) options are Adobe Illustrator, or Indesign. If you are broke you can use the free program available at Create Space. Just make sure that your cover looks professional and awesome. If it does not you might need to hire someone to help you! I know you’re likely broke (most writers tend to be) but you either give yourself the time to learn and make a mind blowing cover yourself or you need to invest cash in someone to do it for you.
I hope this helped ^_^