If your book is cozy fantasy, a warm illustrated cover with small details hinting at the magic system and the protagonist's quirky profession works. My friend's self-pub project initially had a dramatic, sword-wielding hero cover and it bombed. She swapped it for a softer, cottagecore-style illustration focusing on the potion shop, and sales picked up almost immediately. People judge the entire tone in half a second.
Don't just look at bestsellers in your genre; look at the covers of the books your ideal readers actually post about on TikTok or Instagram. The algorithm-friendly cover is often high-contrast, with a clear focal point and readable title in a thumbnail. Serif fonts for historical, clean sans for thriller, playful script for romance. A/B testing on your Amazon ads or even just polling your newsletter list can reveal surprises—sometimes the cover you think is bland wins.