The writer Warren Ellis is writing at length on his discussion web site The Engine about how to market one's comics. I think his principles are generally sound, although having genuine quality (as opposed to "arguable quality") work to offer up seems to make them work much better and I think with certain companies the marketing/pr people do a good enough job that you don't have to worry about entire steps in Ellis' list.
One thing that occurred to me while reading this -- does the self-marketing principle indicate that distributors are no longer doing the job they used to do at the beginning of the "direct market" of comics and related hobby shops? I'm currently doing a comics history that partly coincides with the initial years of the DM, and it's interesting in that distributors seemed at that time to be more directly entrusted with selling the work as opposed to acting as a sort-of seller, sort-of fulfillment house the way Diamond does now. I don't know if that's a function of no competition or merely companies taking it upon themselves to forge certain relationships, but I do find it odd. If you squint at the situation in a certain way, it's pretty easy to see a lot of marketing functions in comics arising out of a failure to demand and get these services from distribution agents.