There are some good sources for writers wanting to learn about the comics writing process. TwoMorrows publishes a quarterly (roughly) magazine entitled Write Now!, which features articles on the process, script samples matched to artwork, and the like. Best of Write Now! features a nice mix of articles from the first dozen issues or so. Peter David has written a book on comics scriptwriting. So has Denny O'Neil. And Avatar Press published an essay by Alan Moore on writing comics (though Moore approaches the problem from a theoretical, rather than a practical, perspective).