This is a bit of a difficult question because you're only really going to get vague answers.
If you're just trying to do this for money, well, you shouldn't go into this with that expectation, unless you know what you're doing. (to be brutally honest) A lot people do this for fun, and its a huge undertaking, even for many of the talented people who do this for a living.
If you're skilled at something, I'd say focus on that. Exceed at what you're good at and compensate for your weaknesses. If you're a writer, then write a great story, characters, or really erotic sex scenes. If you're an artist/3d modeler, create really nice looking characters and make hot/cute as fuck with appealing sex scenes. Otherwise, you'll probably have to download or buy 3D models or purchase art from people to make your game look decent.
Visual novels are an okay choice but I think they're quite common and if your art or story doesn't stand out, people still will like what you made, but don't expect to make tons of money from it. Especially for a first game and if you've never written or done anything like this before.
More uncommon genre's can help with specific niches depending on if you're focusing on more scarce stuff aka Futa/Furry/etc. People will generally appreciate most things, but you should probably focus on genres things you find enjoyable yourself, because you'll at least know that genre is like, rather than something alien to you.
If you're skilled at programming, try using a more diverse game engine and incorporate a simple and fun mechanic to the game, try to avoid grindy and dull combat if possible. An example would be like Karen's Prison or something along the lines of adding sex mechanics to the combat, etc. Try something that you haven't seen before or mimic a good game's mechanics.
And at least for your first game, maybe try something small and get feedback quickly. Focus on trying to get a quality demo going and you'll be ahead of many games, since people tend to leave a lot of bugs in there games (which can upset some people, but is understandable since many of these games are in development). Get something out there at least to see what people think. Get as much feedback as possible, even if its negative, you'll need to learn what you can improve on and what people like. People also really like to see content so if you push out things, people will appreciate that.
My final thoughts, get some inspiration of games or media that you personally like, and try to iterate them, maybe try to improve on things you think should be improved on. Example would be like, you really like Monster Girls and light hearted comedy, well try to write a story or create characters similar to that kind of genre. I think you'll find some success as long as you have something that feels like effort has been put in.
Anyways, I hope that helps. Good luck!