Even if you’re not a professional, you can get close to being one by having an understanding of the actual process of creating books. You can then use your knowledge of what makes a book appealing to readers to help you create covers that are striking, yet still match the style of the book.
A good reader will first look at the title and author of the book. Then they’ll move onto the inside front cover. Next they’ll start reading the pages of the book. When they reach the end, they’ll read the back cover and maybe make a purchase.
Whether or not they’ll actually buy the book depends on several factors, but the size of the cover is certainly one of them. People who have large screens in their cars (phones) do most of the reading these days. So it is important for any book cover to be easily readable.