A really important one I love:
They actually like each other!
Like this seems so obvious, and yet so often I'm looking at a couple going "do you two even like each other?". I'm not saying they have to be a perfect couple that never argues or disagrees (that's equally annoying), or that people who don't get along but hook up isn't great, but if you are presenting them as a romantic happy couple, I expect them to like it each other. But for some reason this seems to be getting rarer and rarer as people confuse sexual tension and flirting and bickering with two people who dislike each other but for some reason you're forcing them together. It's getting to the point where when I see a couple who actually gets along and likes each other and can spend five minutes together just talking and laughing without a, fighting or b, making out, I get super happy.
I love couples who like each other.