I get a lot of questions about how to do DIY cover design, and my first answer is, you don't need to do this if you aren't naturally drawn to doing it. But if this is a skill you want to improve on, but you know that the covers you build don't look like the ones on Amazon's top 100 list, here's a trick: talk about what you see. Sometimes the difference is in image size and placement, but often it's about the text on the page. GET MORE FAMILIAR WITH TYPOGRAPHY.
Five questions I'd ask about other covers that could help you better design your own:
1. What adjectives would you use to describe the title font(s)?
2. Where is the author’s name on the cover?
3. Is the author’s name in serif or sans serif fonts? What letters are capitalized?
4. Does any of the typography on the cover have a shadow or shading behind it to help it stand out? How could that technique be achieved?
5. Are all the words the same size, or have they been shifted a bit to better fit against each other or around the background image?