Here's a snippet of the guidelines from Dark Horse's site:
SEQUENTIAL ARTFull article here.
Consider carefully what you are sending. An editor wants to see that you can draw sequential art, not pinups. Five or six consecutive story pages is usually adequate. Include quiet scenes as well as action, utilize a wide variety of faces, figures (male, female, normal people as well as "super" characters, etc.), and well-realized settings. Ask yourself the following questions: Does the angle you've chosen take full advantage of the dramatic potential in a scene? Do the backgrounds establish where the characters are in relationship to their surroundings and to each other? Is there a well-defined foreground, middleground, and background? Is there a clear, readable story even without word balloons or captions? Have you left adequate room for the dialogue and captions? If you'd like to use a sample script to help you create a story sequence, you can download one here.
It's Week 12 (of 15) of the Women of Star Wars digital sketch card series, Senator Chuchi from the Clone Wars mini series!