Billy Hodges trilogy or Young Samurai ring books (ring of earth etc) few years ago. Unfortunetly I haven’t read neither of these.

Mostly by the cover. Or some other semi-official pre-made art (like I think the Hobbit characters looking like how they pictured in certain comic book). . Some authors describe their characters in clear detail so I just know how they look. Sometimes I compare them to similar characters and think that they look quite the same.