Genre Conventions are important
When you want your book to be noticed by the right audience, the people who want more of what they like, and who don't want to be deceived, you need to have a cover that's genre-appropriate. There are certain conventions that are expected, and though you can play with those expectations for originality, it's not always the right move. There is already plenty of space within those conventions to play with.
For example, a fantasy novel usually has a spectacular moment from the book, or a beautiful landscape, and maybe a painted image; A spy thriller will have bold dynamic font, and smartly dressed characters; A romance will have beautiful characters in wispy clothing; A horror will have high-contrast symbolic imagery.
Consider the effect instant recognition of a genre can have on the appeal of your book. But don't forget this represents what's within your unique creation. Don't copy, but be inspired by, other books of a similar style.
These examples are not real books you can buy, they are ideas for what I could do for you.
Represent Your Content
But don't try too hard to be unique, you may end up obscuring your intent. Don't just make your book attractive to readers, but inform them of its content. They want to know what they're getting. Though a little exaggeration for emphasis won't hurt.
Book covers are not just art, they're advertising. They aren't just a reflection of your book, they reflect you as an author. Like a job interview, you want to appear confident, talented, skilled, and be what they're looking for. Let your book cover represent all that is best about you and your story.
These examples are real books by real authors. Click on the image to purchase and support their work.