According to the publishers, a paranormal romance is a contemporary romance of any kind with elements that are actual (not faked) magic, psychic powers, supernatural creatures, &c. This includes ghost romances, angel romances — where such supernatural creatures are real and have some part to play, including as the hero — suspense romances with psychic h/h, and what are considered the “dark” paranormal romances of vampire romances and werewolf romances — though I can imagine a fairly light werewolf romance involving dog shows. That’s because “werewolf romance” is often the catch-all for romances involving any shape-shifter or skin-walker, whether were-leopard, were-hawk, or what you will.
The trick is that the paranormal element can’t be just tacked on. It needs to be integral to story, whether positively in that the hero’s angel grandmother shoves him into meeting the heroine, or negatively as in the family curse that makes the h/h draw back from the relationship. As well, if this is a hybrid romance, like a suspense romance, the paranormal needs to be involved in the climax. However, in the relationship half, we like to see people resolve to commit to love on their own, though that may be what drives them into the showdown with their external magical problem.
The remaining three sub-genres have one thing in common: the publishers want pageantry. That is, they want the reader to have a strong sense of the time and place not being their own, not necessarily street parades. Use the differences between here and there, especially any glamorous ones. Give the reader a vacation from the here and now.
Historical romances go back a long way, more so than straight historical fiction. Anyone who thinks the field demands strong attention to detail and tons of research hasn’t read what’s being published. Now, these half-baked items are not going to be immortal — they’re quite throwaway — but they’re published and paying for a nice vacation. These are not the Big Books, but the least bad ones that Harlequin Historical got sent last year. They have an automatic need for four a month, and at least two of those Western romances in particular. If you can write about the cowboy finding a wife, over and over, you have a career (or the marshal, gunslinger, or Mountie). If you want to be a Great, though, like Georgette Heyer or Nora Lofts, you’ll do the research.
The Regency romance, set in English society, time limits by the publisher but loosely 1805-1830, used to be a huge deal. It seemed like a third of the historicals were. The field nearly died of becoming ingrown in the 1990s. People never did research for their books any more, they just read other Regencies to pick up the lingo. The Jane Austen revival has kicked those over to the curb, and one really just finds historical sweet romances set in the Regency.
I can never understand why anyone writes any form of historical fiction who doesn’t love reading about the history of everyday life. It is so much easier to turn to ahistorical fiction.
It’s a whole ‘nother form of research to write romances that require world-building, but once you have done it, it works for all the others. That is, if your true love in writing is medievalesque heroic fantasy, once you know how a few variants on medieval culture and economics work, besides worlds in general, you make up the details, and different systems of magic for different worlds, but you don’t have to go back to the books the way you would if you set one story in 1200 in Syria and the next in 1350 in France. World-building is just considered easier.
The first of these is the fantasy romance. Big pageantry, impressive magic, uncanny danger — or maybe some slightly screwball family curses, usually in a medievalesque world (one reminiscent of the Middle Ages and Renaissance in Europe), though a kind of steam-age, Victorianesque world is showing up, like a Regency romance with wizards or lordly elves. Quests or Machiavellian politics are the basic motivators, maybe both.
Futuristic romances go to the other end of time. Unknown worlds, not Earth, but not magical, either, wind up here. Sometimes it’s a colony of Earth that has gone its own way. More often, these are set in interplanetary societies, either of our future (yay! you can use Terran-descended names!) or those of which we may be the lost colony, if Earth is ever mentioned. And though it isn’t strictly the future, if your protagonist gets plucked off Earth by a UFO and carted off into the interstellar society we don’t know about (probably never to return), that’s a futuristic, too, when you’re selling it.
The time-travel romance is a great way to get someone kind of like the reader into one of these three kinds of worlds. Yes, 85% have to do with the heroine going back in time to meet one of those old-fashioned hunks, 2% have to do with men of our time going back. The small minority are trips forward, and I haven’t seen a cross-time story yet.
With all these, you stick to the Romance template. The story is at least 50% the romance, if not more. The setting is there to create obstacles to the romance, because in other worlds and back in time you get to use the good old stuff, like, “This marriage was set up in my father’s will,” or other unavoidable family pressure, marriages of state, forbidden line-crossings (really, we have none today, for enlightened readers), a hero or heroine who needs to kick over the unenlightened rules, &c. The solution to the romance barrier, though, should not come out of the setting (the temple seer/watching computer tells the h/h they ought to trust and reveals all their secrets to each other), but out of the characters’ decisions. The other is a stinkin’ deus ex machina, which you should avoid as a plot-killer.