Make the comic. Unlike book and magazine publishers, comic book publishers are primarily interested in seeing a finished product. Submitting a query letter or project outline is unlikely to generate interest. If your strengths lie in writing rather than illustration (or vice versa), consider working with a partner.
Research your market. The annual Artist and Graphic Designer's Market publication (see Resources below) contains listings and contact information for many comic book companies. Review the listings and choose companies looking for work similar to your own.
Prepare your submission according to the publisher's guidelines. If you are unable to find this information elsewhere, check the publisher's website. When submitting your proposal, don't forget to include a self-addressed stamped envelope.
Attend comics conventions. Conventions are an excellent way to network with comics professionals and learn more about the process of breaking into the industry. Always bring a portfolio or a copy of your finished comic.
Self-publish. If all else fails, consider self-publishing. There are many options for self-publishing at your disposal, from print-on-demand services such as Lulu (see Resources below) to online publishing. These options often include additional means of generating revenue, such as advertising and merchandising.