The largest (and hardest) part of a good collaboration between a writer and an artist is communication. There’s nothing like seeing the story and the characters you imagined fully realized on the page, but there are lots of points along the road for that to go wrong.
Think of the last time you saw a movie based on a book you had read. How much did the person on the screen vary from what you thought you read on the page? Description is largely about degrees and while it’s easy to overdo it and leave your artist no wiggle room, it’s also easy to underdo it. If you forget to tell the artist the color of the character’s hair or the way a character stands, you may lose something. Worse yet, somebody may have to rewrite or redraw something when the two visions don’t gel.
Jules Rivera is one of the most communicative artists I’ve had the pleasure of working with. When she was designing a younger Bedelia for her short story, she wanted to make sure that I was happy with the way things looked and that it didn’t conflict with my vision of the character. What resulted was a great short story and collaboration.