3 Years of Service
I can't stress this enough. It doesn't just apply to adult games, it can apply to any story driven game, or even writing. You should ALWAYS have at least a general outline of how you story will play out before you even begin full production. If you are going to branch the story, have the branches at least somewhat figured out too. I've seen too many devs and writers write themselves into a corner, and end up A) dropping the game, B)having their story wander all OVER the fucking place, or C) rely on a Deus ex Machina to get their characters out of whatever bullshit scenario SOUNDED like a good idea when they began writing it 3 updates prior. I'm not saying you shouldn't add things, for example, you are writing and there is an event that you realize would be a good opportunity to put a new choice/branch in there. Awesome. Now, before you actually implement that, figure out how it plays out before you do any art or coding.Know where your story is going to go and how it is going to end before you start.
Another point.. STAY CONSISTENT! Not just with a release schedule, although that can be important too, but throughout your game. Keep the art consistent, keep personalities consistent, keep the rules of the world you are making consistent, and keep your game-play consistent (if applicable.) Don't do a straight VN for 7 updates then all of the sudden make your players have to complete a shit ton of mini-games to advance the story.
There are exceptions to every rule, but trust me, 99% of the time, your game is NOT the exception....
UNLESS that content is the central focus of the game, then put that front and center so that those who don't like it won't waste their time, and possible even get upset and go on an internet war against you3) If you are adding content that is a lot more niche (scat for example), allow players to opt out.
Just my 2 cents worth