Write what you love... not what you think will sell.
Every author is different, but this is just my two cents and how I personally approach my own writing. We all have to bring home the bacon, so sometimes what determines that decision may be how heavily you rely on the writing income and how your sales are. Which for me, sales are pretty much like going on one of those roller coaster rides where you throw up at the end.
I'm writing this because I had another inquiry yesterday on this, so I thought I'd address it. I've had a few people urging me to write a straight romance (one of my good friends has noticed I've grown a little testy about it..lol). Why? The explosion of NA books hitting the bestseller lists. Kudos to the writers who hit the lists (it's tough work!), because for every person who has, there are probably 500 who did not. Unless your speed writing, I don't know how a person can keep up with the trend. Being on the Barnes & Noble top sellers was uber cool, but it's not what drives my writing. Plus, if I did write a straight romance, I wouldn't like be likely to include some of the dark matter that's in these books, because I'm very sensitive to that kind of thing, so I wouldn't really be following the popular trend, now would I? :-)
Someday, near or far, I will write other genres. After all, I started off writing straight fiction. I'm too passionate about the stories I currently have on my plate to go in a different direction, and I have so many projects in the pipeline! I could easily eliminate the paranormal aspect and broaden my audience, but that's what makes it so exciting to me! I love the twist it adds to the story, and I also enjoy writing it in such a way where it doesn't dominate the book, and at the end of the day, it's the characters that are still driving the vehicle.
The coolest thing is when a reader says they've never read paranormal before until this series, or it's unique and not what they had expected. That's the best compliment evah.
Trends are cyclical. Two months from now, thrillers make take off, or dudes in kilts who are bookalicious. (although let's face it, those hot men in kilts always seem to do well..heh) The current romance trend often deals with very heavy topics, and readers will eventually seek out fantasy escapism books because of reality overload.
I think it was about a year or more ago I saw an author (who didn't even write in the romance genre) post they were going into erotica because they read 50 shades. *face palm* Writers should be well read in the genre they're writing to understand it; I don't think reading one or two books qualifies you as an erotica writer, romance, or paranormal. We all need to branch out to a degree (although I don't think I'd want to see Stephen King try his hand at romance simply because it's top on the charts...holy egads, that might be the scariest shit I've ever read! I'm still a little disturbed over Gerald's Game, but I digress..) but how is your book not going to feel like a million others? No one wants to write that book that someone will describe as "Oh, it reminded me of xxxx's book, except instead of a bus they were on a train".
Noooo! Kiss of death.
Unless they sold a million copies. Then maybe it wouldn't sting so much. Although for me, it still kinda would.
When I started writing with the Mageri series (and onward), I actually approached writing in a way I never had before. (Blame this on my early exposure to apocalyptic books). It's a great method!
I wrote the books like no one would read them. No one. Evah. I imagined that if an apocalypse came that wiped out all of humanity and every single book on the planet, I would have a very large bookshelf that was empty. I would live out the rest of my days alone, and the only entertainment would be the books I wrote. I needed to fill that shelf with books that I would reread over and over, stories and characters I loved. So I poured everything I had into those books from a perspective I hadn't before, where I eliminated the reader and wrote for myself. Thanks to Rod Serling and Earth Abides, I created a new world using that perspective.
Of course, the characters always take over the story at some point, but that can't be helped. I thought that was a really cool way to look at it, and to not focus on any other outer influence. There are always outer influences at play: The voices in our heads, the current trends, movies, music on the radio, our favorite authors and how they would write the book, what readers want or expect, the genre formula, wind gusts and humidity....
You have to be able to separate inspiration from influence.
"Closer" was a romance with a paranormal kick, and I liked that because it gave the story a unique setting and challenges for the characters. "Seven Years" is paranormal, and I'm really excited about it because I think that there are scenes that work so well because of the paranormal aspect that wouldn't otherwise.
At the end of the day, it's your time and money. Make sure that bookshelf gets stuffed with stories that you love, and your readers will love them too. (Whether it's 2 or 2 million)