How to write just enough but not too much
Question: When I asked a similar question you said sometimes less is more like with torture or sex scenes. Well in my book I have a sex scene and I was going to do the beginning and after but I'm not sure how to do the beginning. How much am I supposed to do for the beginning? How much am I supposed to describe?Answer:
You know better than I do who your ideal reader is. Put yourself in their shoes. What would they want to read? What would address their interests, feelings, situation, etc. Remember, you are trying to please your reader first, not necessarily their parents, teachers, or clergy. At the same time, don't give them something so graphic they put the book down.
There is no "supposed to" about this. You must be true to the story and speak to the reader. Trust your emotions. If it feels right to you, you can't do any better (at least not in a first draft).
Let it rest for some time, then read it again and make a second draft.
Once you have something that feels right and has been revised a couple of times, consider showing it to someone--a critique partner, someone similar to your ideal reader, a writing group, etc. to get their reaction.