A book's title lives in your reader's head long before they open it, so I always hunt for a phrase with multiple hooks. Mine the manuscript itself for a line of dialogue or a recurring image that carries thematic weight. That central, ominous object in 'The Goldfinch' or the raw, visceral command in 'Gone Girl' didn't come from nowhere—they were buried in the text, waiting to be the flag planted on the cover.
Practicality matters, too. I search online retailers to see what else shares a similar name; you don't want to get lost in a sea of identical thrillers. Testing a few frontrunners on a trusted reader can reveal immediate, gut-level associations. Sometimes the most evocative title feels a bit strange at first, but that strangeness is what makes it memorable and uniquely yours.