Although I've been running a romantasy class this month, I think it's important for writers to know that just because a genre is trending doesn't mean you have to stop everything and bow to it. I've seen complaints in social media from agents noting that no, not everything is romantasy.
Obviously, if you have some ideas about whatever is trending, you can give it a shot. Readers are voracious beasts. Once they're hungry for something, it'll be hard to satiate the reading binges for whatever the trend du jour happens to be. However, if you're strictly urban fantasy or paranormal, you want to avoid trying to bend a perfectly functional story out of shape.
Trends come back around. Vampires are making a comeback. And romantasy, trust, existed before the portmanteau. Fantasy readers just didn't have a means by which they could directly indicate a blend of fantasy with a major romance plotline. This means that whatever you actually want to write will probably come back around as well. Thus, creating a strong backlist might be a better choice in the long run, if your offering for romantasy was going to actually be an urban fantasy wearing fairy wings.
If you DO want to try your shot at romantasy, here are few notes on the genre:
1) Look on some online forums where they talk about romantasy. Try Reddit and watch a few Booktubers who list their favorites. Read a few of the recommended books that you might like and fit your brand and style.
This isn't to COPY but rather to recognize where you might fit and what tropes YOU enjoy enough to sustain you through a writing project.
2) If you aren't used to writing fantasy, take extra care in your worldbuilding. This is where "doing it for the clock app" books fall apart. The worldbuilding is thin. It doesn't make sense. It contradicts itself.
Consistency is critical in worldbuilding. And fantasy readers expect to be able to get lost in your world.
3) As a consequence of all this worldbuilding, romantasy may have more information to convey to the reader than you're used to if you're not coming in with some fantasy background. Be careful about either dumping too much information or not being clear enough.
4) Remember also that while romances have trended first person, fantasy has long trended in third person, especially third person with alternating perspectives. Keep this in mind and choose what will help you fully convey your story.
5) Determine the level of spice and romance in your romantasy and make a distinct effort to 1) balance this within your narrative and 2) indicate this to your readers. Books range from the flaming hot to the completely chaste, and not just the YA.
Everything's fair in love in fairies.
