read what i wrote... "don't mush it up with lovey-dovey stuff that would only fly in the p/b romance market..." the kind of soupy-goopy stuff you'll find in romance pbs sold at the supermarket checkstands will not work in a shoot 'em up... and all combining them would do is guarantee that no one will publish it, because neither the guys who read clancy and coonts, nor gals who read silhouette and harlequin will buy it...
actually it's an art 'medium'... 'genres' are the types of fiction you might write [such as western, erotica, fantasy, et al.] and if your goal is to make a living as a professional writer, you do need to write what you think will sell, to some extent...
To some degree. I'm a product of the market; I read a lot, and I read new things a lot. Things that are "trending" in the market at the moment, I'm likely to have read, be reading, or read soon. What I write is influenced and inspired (to some extent) by what I read. So the fact that "Urban Fantasy" is booming as a fantasy subgenre at the moment means that I'm reading more UF. Since I'm reading more UF, there's a greater chance that UF-inspired ideas or concepts are going to be expressed in my writing. So yes, I do follow the market, but it is an organic-type following, not an artificial modification of my writing to fit what I perceive to be the current boom.
If you're writing for a recent market trend, keep in mind that by the time your book is published, that trend might already have faded away.