Or, Once more with feeling....
I understand that behaving professionally might collide with author dreams of making three separate best-seller lists at the same time, but unless you really are Stephen King, it's not going to happen. So stop, breathe, and thank God if one of the 1200 or so credible literary agents in this country actually want to work with you.
Most of you got this on the first go round, but a handful still don't get it, so I'll try to S-P-E-L-L it out real slow. Unless you have been published in reputable book form, YOU ARE UNPUBLISHED. Almost every first novel I have ever sold has needed work - a lot of work. Usually two rewrites guided by me, and then one rewrite guided by the editor. Until you have been through that process, everything you write whether it's science fiction, horror, romance, young adult or literary fiction, will need editing. If you are writing non-fiction, I will also have to guide you, even if you've been writing articles for The New York Times for over a decade (possibly more so if you've been writing for the Times for a decade). You don't know how to write a book. You don't know how to pace 300 pages. Believe me, I know.
Once you've sold a book and you look at what you wanted to send out without that editorial guidance, you will want to change your name and gender. So having three books that need work go out in different genres, probably isn't going to help establish you as a writer.
Agents also guide your career. They will tell you what genre you are most likely to do well in. After your first sale in that area, you should do another title in that genre. Then, if you really must show the world that you can write martial arts fiction and picture books, by all means give it a whirl, but don't be surprised if you don't get an offer or if the offer for your first work in another genre is much less than that in your established genre.
So yes, many of my authors who write both fiction and nonfiction or romance and horror or mysteries and sci-fi, or even erotica and YA, but they establish themselves in their best field first and then go from there.
Is this clear?
In the case in the last post, the author says the second novel is a "dark literary" novel, which usually is a pretentious way of saying a horror novel that I want you to try selling in hardcover. It is not as if he's selling SF and romance. I am sure Mr. Famous read it and said, "this needs a lot of work. Let me see if I can sell what I have." Agents usually work on one book at a time, unless they're willing to handle your nonfiction and fiction.
Editors also work on one book at a time and publishers and editors get kind of pissed off if they find out they are making an investment in you and then that you have these other book commitments that you never bothered to run by them. When you actually have a contract, then you can go to another editor/publisher and say GREAT AMERICAN NOVELIST publishes horror at NAL, but they don't want to do his romance, so we're looking for another publisher in this genre. But it's not done before that because you don't know if you're any good in horror.
If one of my clients writes something that's not for me, and I think it's publishable, I'll refer them to another agent who handles that material and the other agent and I will work together.
We expect you to know what you're best at.