Went down a rabbit hole on this last year when I was trying to title my fantasy series. Turns out, a lot of people just scroll past titles that sound too generic. You need something that hints at the core conflict or a unique element without giving the whole game away. 'The Poppy War' does this well—it's specific and evocative, but you don't know what it means until you read. I spent weeks checking Amazon bestseller lists in my genre, not to copy, but to see patterns. Thrillers often use short, punchy titles with a single compelling word ('Gone', 'Sharp Objects'), while epic fantasy leans into symbolic objects or locations. The biggest mistake I see is titles that are forgettable because they're trying to please everyone.
Also, say it out loud. Does it trip off the tongue? Can you imagine someone recommending it in a bookstore? 'Have you read The Seven Deaths of Evelyn Hardcastle?' works because it's a mouthful that makes you curious. My early drafts had titles that were basically loglines, and they were awful. Keep it tight, give a flavor of the tone, and make sure it doesn't already exist as a famous work. A quick Google and Goodreads search is mandatory.