1. Money. Don't enter your 30's without any savings! Start saving money in your 20's. No matter how bad it gets.
No matter your marital status, always have a bank account in your name.
No matter how good your relationship /marriage is, always have your own get-away fund.
Save 10% of anything you make in a special saving "pocket". Save an addditional 5% in a separate "pocket" for anything you suddenly need to buy. It might seem like very little, but it will accumulate in 10y, trust me, you'll thank me later.
2. Education & languages. Education in Europe is infinitely more affordable than it is the US. Start learning a foreign language in your teens (or sooner if possible!) Preferably French / German / Spanish / Italian. This will enable you to get your Bachelor's Degree without going into debt, and also have an amazing experience. Some never travel back.
3. Marriage. Don't get married young! Especially not to leave home. Even if you love your partner and seems right. Don't marry before 25. IMO it is best to marry for the first and only time in your early 30's, but depending on when you want to have kids, it may shuffle.
4. Leaving home and starting your lofe.
If you want to leave home and you have no money and nowhere to go at 18 - that's normal. You don't have to join the army/marry/get a slave job to move out.
Go on aupair, or any other program, volunteer thing that takes to a new geographic location. I hope these options are made available again after the Coronavirus.
5. Cheating. Truth is, if you're cheating. It actually could be because you're with the wrong person. It's not their fault, but it is ^them, and it unfixable. If possible, leave. And do NOT tell anyone
"Once a cheater, always a cheater". Might be true for some, but wasn't for me. Although I did cheat with one partner, who just wasn't right for me, I was committed wholeheartedly to another partner, a much more sexually and romantically giving partner, with whom I've been longer with, by now.
Some people act, as if cheating is worse than murder, and if you cheat, do not tell anyone. True, some people are borderline sociopaths and they will just fuck anything like weasel, and justify their cheating with gender bullshit, but I felt like shit and it made me realize I need to leave my partner at the time. It was a horrible, slow process.
6. Sex. The best sex could be with the wrong person and good sex can cloud your judgment. I wish there was a correlation between how right a person is for you and how good the sex is, but it's just not how it works. I had my first gushing wet orgasm with the wrong person at the age of 24, and thought I must have a relationship with him now. Big mistake. It will take some time for me to figure out he wasn't even that good, it's more about how unconstrained I felt that made orgasms possible.
Learn your body, get a toy, learn what feels good, otherwise you'll end up following what the guy thing is plelasurable for you and many guys rely more on the psychological (control stuff, anal, threesomes) than the physical (clitoris stimuli, angle of penetration, smell, touch - all of which are actually a lot more effective than hair pulling)
7. Contacts. Make the effort to keep in touch with competent, valuable friends. Send texts and messages or the occasional cat meme just reestablish your presence in their lives.
Do NOT send nudes by which you can be recognized. Remember, we have a times on our cameras, so your face can be framed out or obscured. Wigs or hats, if your hair is distinguishable.
All the money, love and success to you.