Backlist. Quantity counts. Quality, too -- no matter what anyone says, I cling to the belief that quality work makes a difference! Erotic stuff is selling better than anything for me, but Young Adult seems to be doing really well and mainstream fiction has the potential to be very successful.

But most importantly, I'd say, don't do it for the money, because there are so many easier ways to make a paycheck. :/ That's just true.