Rule 1 of any design is to have a distinct silhouette. This means that a character should be recognizable even if they were blacked out, or well, silhouetted.
Otherwise, I don't usually factor personality into the designs. Many of my characters do not have designs that reflect their personalities, in fact many characters have designs which clash with their personalities. Instead, I factor personality into the poses, and even those may not be reliable as some of my characters may be faking parts of their personalities.
For instance, I once thought of a character who's behaves in a stepford manner. Her appearance, behaviors, and mannerisms in concept art would reflect as such. However, I had the plot twist that she was a cult leader of some sort, and she gleefully facilitated human sacrifices.