The theme. The character. The genre. The mood. Any and all of the above.
Take a line from the story. Use a mix of character name and genre. Pick something that appears, predominantly, within the story – a centrepiece.
Long or one word, but keep it identifiable to your story. Allow it to roll easily when said vocally and mentally.
Be prepared to change if it doesn’t match your final story.
Think of a promised clue. A statement.
The title belongs to the entire group of words you blended onto the screen.