I'm assuming male mc.
-the core of drama in the genre is that the women in your family will always try to resist and avoid any sexual situations with the mc. the job of the player then is to find the way though their defenses using trickery, affection, corruption, coercion or violence, depending on the type of story. doesn't matter if it's a love story or a rape fantasy, the women should always refuse and resist mc's advances. even if they secretly want him.
-don't ever make them slutty. even and especially if they're strippers/prostitutes, you MUST do your best to portray the normal person behind the job. that's the trick.
-don't add random secondary fucktoys for early sex, they just undermine the value of that final goal of family pussy and burn you out (as dev) before you get to the ACTUAL girls you wanted to write about.
ask yourself: "when I'll inevitably abandon the game around v.03, at that point, do I want to have finished sex scenes with mom or some random non-relative friend?" because you won't have energy to do both.
-if you have a secondary plot beyond the incest one (like mob plots, business plots, mystery of how dad died etc) NOBODY gives a fuuuuuck what happens in it. every second you force people to read it will make them groan or fastforward.
you can still use a secondary plot to help writing your incest scenes inside it, it WILL make writing easier because you have a direction, but do not for a second think anyone gives a fuck where that story goes. they only care how to advance the relationship between mc and his family.
-moms should be MOTHERLY. that's their only job in an incest game. they don't need to be homemakers, they can just as well be career mom's etc. as long as it's some kind of a 'mom archetype' the audience can recognize. you need to first sell audience her 'momness' before you can violate it.
-sisters and aunts have much more leeway, but they still need to portray recognizable family roles. cliches and tropes are your friend, they're the language that allows you to convey audience "this hot piece of ass with her pussy showing is his relative".
there's probably a million other things but these are the IMPORTANT ones that make or break your story. nobody who looks for incest stories wants to see some random hot sluts jump on mc's dick, they look for a convincing simulation of home life and THEN perversing that with sex that shouldn't happen.
