What are the best ways to approach marketing a novel under a pen name?

You could always put in, "Prelude (Forward, etc.) written by Cristina Hartmann". And make a fairly large intro chapter for the story. Then list your name as a coauthor of the first book in the series on any marketing or websites you have setup. Your fans may or may not figure it out but then you can market that you wrote the prelude to your fans in an effort to get them to buy it... Thus you are also endorsing this "other" author as being a+ in your mind..... Especially in your mind...

This problem has come up before, and here was Kurt Vonnegut's partial solution...Kilgore Trout. See artilcle about this ... http://en.wikipedia.org/wiki/Kilgore_Trout ****** Pick a pen name that is "somewhat obviously" a pen name but which is very memorable. Don't use "B . Traven " Good examples would be the singers named "Englebert Humperdink" "Elvis Costello" The wrtier / gossip who goes by the name "Perez Hilton"   (and got sued by Paris Hilton, BTW) The actor Paul Rubens, went by the name of one of this stand up characters "Pee-Wee Herman" ****** Okay, let's brainstorm some names... Podkayne Trout    combines the name of a character from Heinlein novel with Trout  http://en.wikipedia.org/wiki/Podkayne_of_Mars Eleanor Ripley     This is a bit more subtle (maybe TOO subtle) playing on the Beatles song Eleanor Rigby  but changing the last name to that of Sigourney Weavers character in the Alien movie. Barbarella (Barbie) Princess   Could work well if there are some funny quips about critical theory, role models, and a hipster attitude. For a dystopian novel, some of the clasical name will work well, like Medusa, Electra, but best of all  -  Cassandra Cassandra Spengler    Classical / Historical /Literary (Oswald Spengler wrote Decline of the West ) but something more obvious, like  Cassandra Orwell might work much better. Or, you just go gonzo with something like - Barbie Armageddon. **** Then consider Ariel's and Erica's advice for cross promotion.

If the main reason for using a pen name is to keep genres separate, then you may want to consider making your pen name transparent. Either use a variant of your name (with middle initial, maybe?) or be open about the fact that you're "writing as..." On the other hand, your credibility under your real name may not be all that relevant, depending on how different your genres are. If they're so divergent that there isn't going to be much of a cross-over audience, then you are starting from scratch, whether your pen name is transparent or not. The best thing you can use, I think, is not your credibility, but what you've learned about marketing and promoting yourself. Make your pseudonym a twitter account, a facebook fan page, a goodreads page, an amazon author page, and maybe even a tumblr or a blog. Cross-promote yourself, and use the networking you've done and any contacts you have in the genre, for blog tours, interviews, maybe some book giveaways.