I've always liked stories where the Woman/Girl isn't completely naive. Like Men/Boys they are aware of sex they just haven't had it. So there won't be:
Girl: What are we doing?
Boy: Fucking
Girl: What's this called?
Boy: A Pussy
Girl: Fuck my pussy! Cum in me, and knock me up! and after that I'm going to take you and eight of your friends and I'm going to....
They just don't turn from, innocent girls who never knew sex existed, into porn stars overnight.
There will almost always be, unprotected sex and Impregnation or the chance of it, possibly incest but never the fath/daughter type, never water sports, and maybe bestiality (the thought of someone horny enough to have sex with animals ie. woman/dog turns me on, but I have never and never will do it, so its kind or hard to write about something that I know nothing about.