Everything I learned about life as a kid was wrong. I mean, aside from objective facts, all the theories about how life is "supposed to" be were wrong. Some of them were outright lies, but most things were just misunderstandings handed down by people who had been taught the wrong thing when they were kids.
The thing that comes to mind most is sex. As a woman I was supposed to protect myself from sex, my sexuality, and especially the sexuality of men. Sex was gross, or immoral, or meant only for the confines of an intimate relationship (preferably one that was legally binding). Men were sex monsters*, to be feared, and they didn't care where the sex was coming from, who it was with, or if that person was enjoying themselves as long as they were getting their rocks off. Now, when I was being taught this lesson, most of the adult men in my life acted like this was true and I had no interest or ability to find out otherwise until later in life when I actually started having sexual relationships with adult men.
The other thing, was that I was on birth control "just to control my periods", cuz I was a "good girl" and "didn't do that stuff". Which, for the record is mostly true. I did not have PIV sex until I was 18. I wanted to be an adult making my own decisions about what I did with my body before I started having "real sex", because I thought that was the best course of action. I can't say if I was right or wrong on that because I don't have a measure for comparisson. I once told a friend that she would never regret not having sex with someone. I don't know if that's actually true, but I do know that if you're kind of hedging on whether you want to or not, you probably don't really want to.
I think that's the main lie we tell young women about sex: your feelings about the performance of sexual acts should be mixed. But the thing is, when you want it, there are no mixed feelings, and there's no real way to create that conflict if it doesn't exist in your mind. Sometimes in a long-term relationship, there's a sense of duty attached to sex**; and sometimes it's okay to have sex with your partner simply because they want it. Of course, we're taught that this is how things are "supposed to be", not that this is something that happens sometimes, but that it's better if your feelings are clear on the subject of doing the sex together. [A side note here: it's really hard not to sound moralistic on this subject. I don't want to shame anyone on this subject because life is hard enough without some broad on the internet telling you you're doing your sexual relationships wrong.
I have a number of young women in my life, and there are things that I want them to know about sex, how to treat themselves regarding it, how to expect to be treated by their partners, etc; and it's really difficult to have that conversation with anyone because it's fucking awkward. A lot of the time, young women and girls have been taught all about saying no to sex, and preserving their purity, and all that blah, but we don't talk about saying yes to sex. We don't talk about masturbation and how it's totally okay to touch yourself "down there" and not call your vulva "down there". By and large, we don't talk about how it's totally okay for women to enjoy sex; to the extent that there's still a debate about orgasms for women. And nobody in any sex-ed class ever ever said that pleasure was an important part of sex. And it fucking is.
If I was to tell my granddaughter or my sister (or any person for that matter) what I think is most important to a fulfilling sexual experience, it would be three fold:
1) WANT it: don't go along with it just cuz your partner wants it (obvious), but don't hide the fact that you want it either. Sex is an important part of the adult human experience, and if you hide your desire from yourself or from your partner you're gonna have a bad time. Don't let anyone shame you for having sex cuz you want it, or for not having sex cuz you don't. It's your body. You are an adult capable of making decisions on what to do with it. Own that shit.
2) Talk about it: It's almost a cliche in my world, but communication is the most important aspect of a relationship (no matter the duration or context). And I'm not just talking about the safer sex conversation (condoms, lube, STI testing, boundaries), that stuff is great, but it's also so clinical that it takes the fun out of something really awesome. Once you experience step one of this equation (wanting it), tell your partner. I promise you that, provided the feeling is mutual, it will be a serious turn on.
3) Enjoy it: Scientifically speaking, because humans retain the ability (and desire) to have sex long after the ability (and desire) to make more humans goes away, sex is not a process that is solely for procreation. It's fun. Or at least, under ideal circumstances it's highly pleasurable and results in better sleep, better skin, lower stress, and a deeper*** connection with your fellow human. Orgasms are awesome, but you don't have to have one every time in order for ever sexual encounter to be fun. Lots of people never orgasm in their lives, lots more still don't orgasm every time they have sex*', but most of those people still enjoy having sex. Like a lot of things in life, the destination is not nearly as important as the journey.
That's my advice: want it, talk about it, enjoy it. If something isn't clicking, communicate. If you're not having fun, say something. It's hard to talk about these things because they make us vulnerable, but vulnerability is the beginning of intimacy and that makes life way cooler than cynical stoicism. Intimacy (which in this context is not a euphemism for sex), whether it's with a new partner, a previous partner, a long or short term partner, or someone you're with just for the night; is pretty fulfilling. And while it isn't something you must have in order to have an enjoyable sexual experience, it does make things more fun.
I think it's time we stopped lying to our young people about sex. Really, stop lying to them in general, cuz they're gonna figure it out and be kinda pissed when they realized we thought we had'em fooled. But the sex thing is really important, because sexuality is an important part of becoming a functional adult. I think a healthy grasp on your sexual agency is more important to adulthood than paying your bills on time.
Anyway, here are a couple of books (currently living on the bookshelf behind me, even) on this subject that opened my eyes:
And the sex scenes in Atlas Shrugged by Ayn Rand (cuz those are really fucking hot, and say what you will about the rest of it, Dagny Taggart is a sexually assertive woman and Rand deserves some credit for that particular aspect of that particular character).
*This idea bothers me a lot. See this piece for a beginning of a reason why this is a problem.
**Which I think is at least partially responsible for monogamous women losing interest in sex with their husbands.
*'For the record, my definition of sex is any activities that make orgasms more likely/possible.