One of the most important parts of creating a comic is thumbnailing. Making small, quick sketches of what you imagine your idea to look like, and trying out different ways of showing it. The real value in thumbnails though, is to find out how your characters should be posed, how much of them you should have to draw, and where they should be in relation to each other and the text. It's a tall order, eh?
So here we have our two characters in a pretty standard side to side composition, but from the thumbnails I have decided on two things. For my idea Cortana has to be giving the Chief a raspberry (what a tart), and the Chief will be leaning down, pointing at her accusingly.