John Rozum has a cool post on "casting" his characters in his head before he writes them. Referring specifically to Adam and Julia Kadmon from Midnight, Mass. he talks about how imagining a specific actor in the role can not only help communicate ideas to comic book artists, but can also help solidify the character in your head as you're writing:
When I got to thinking about Midnight, Mass. again shortly before it finally became a reality I had an epiphany of Julia being Famke Janssen which really brought together all of the loose threads and ideas I had for the series and definitely cemented the character of Julia for me.I've done this a couple of times and it was very helpful. I need to do it more.