I mean, it's tempting to be flippant, but I think the true answer is: "Provide something people want, but don't have".
That's easy. Doing it is hard.
It could be dancing close to the edge, to provide as close to 'taboo' content as you can get away with, while still being paid. There's certainly a market for that, and because those that dance across the line get smacked by Patreon/Paypal/Steam/(or even here, in the case of some rules), there's always a space for that content.
You could be creating furry content, or gay content, or furry gay content. Because not a lot of people do that, and the people who are really into that are REALLY into that.
You could be making romance sims about being epic and loved (like I do), because western media has decided that the old stories of being epic and loved aren't upsetting expectations enough, and now everything is supposed to be grey and miserable.
You could be making happy stories that make people people laugh, you can make ones that make them cry, you can make stories where the MC enjoys sexually torturing people, or one where the lewdest moment is handholding, and a stolen glance at a wet t-thirt. None of that defines success.
To be successful, I think, you need to create something you personally enjoy, and believe in, while being fresh and interesting for SOME people.
I can't tell you how to be successful (sorry). I CAN tell you how NOT to be successful. If you go look at the top 10 games, and make a game where you're a young man that moves in with his "family" in a new city where his bitch "big sister", naive "young sister", and prozac-abusing "mother" are all wanting to fuck you, you'll find that niche is already over-filled.
So go make a game that excites you, that fulfills some under-satisfied niche, and that'll make people happy.
Easy to say. Hard to do.
Good luck.