- Science and technology: do I have to worry about tech if I'm writing a romance? Yes. At least enough so that a reader isn't thinking "But we have X now. How come we don't have X 60 years down the road?" You don't need the same level of detail a science fiction reader expects, but at least explain why the planet/starship/base has no ground level or satellite level defense systems, if you've decided that it's all humans/all the time. They can malfunction, they can have proved ineffectual, they can be not germane to your plot, but do consider why something is or isn't there.
- Science fiction and relationships. Your sexual and romantic relationships should not be based on 1950s U.S. heterosexual standards without a good reason. Transfolks, genderqueer, LGBTQ, asexual and intersex people all exist now. Some are welcome in sundry armies, navies and so forth now. If they're not in your m/m or f/f or m/f, etc. military story set in the future, why not? This also goes for people of different cultural and racial backgrounds. You can't write believable aliens if you can't write believable humans, just saying
- Relationship development (most a romance/erotica problem). "I've spent three hours with you, been unconscious for an hour and a half of that, think you killed my best friend/parents/pet and yet I'm totally drawn to you and suspect I'm in love/lust." Really? Alternately: "My spouse/lover/BFF just died horribly. I've known you for the narrative equivalent of 20 minutes. You must be my new soul mate!" Now compare that to any romance, erotic or otherwise, by an established author. There's trauma and recovery and doubt and a significant number of complicated emotions on the way to that happy ending, of whatever sort. Go now and do likewise.
- Word choice. "I do not think that word means what you think it means." I see this a lot. Look things up and double check. We all have words we consistently misspell/misuse. Watch for your patterns.
- Transgressive sex scenes. Consider who you want your audience to be. Rape, in the absence of a character dealing or not dealing with trauma and violence, is not "character building" nor is it "character development." Even more esoteric brands of consensual sex can have high squick factor. You may want to get that reaction but be sure that is what you want. Don't do it by accident- think about why your characters are having or not having sexual encounters and what impact you want those encounters to have on your story. They'll be much more effective and it will make you a better writer.
- You want to write? Read in the genre you want to write in. Read books and stories by people you don't know. Read authors from cultures and countries different from your own. Read stories written by authors from orientations different than your own. You don't ha e to love all of it or even finish things you don't like, but you will be a better writer if you know your field. Really.