For the first seven years of life, a parent teaches a child everything they can. In the second seven years the child starts to listen more to peers and occasionally teachers. In the third seven years, it has to be very simple to get a boy to pay any attention at all: three things.
So Jack, in the event I'm not here to tell you these things, pretend I am. Pretend I walk with you through your days saying:
You don't know everything
You think you do. As the brain wires itself for the final time around 14 or 15, you discover all the horse-power you have and mistake it for wisdom. You can now think like an adult, but you do not have the store of experience of an adult, to teach you a little humility and eventually a smattering of wisdom. And you are still accumulating the collected wisdom of your species.
The thing that differentiates us from other animals is language. Real language, not just a variety of barks or grunts for "food" or "danger" or "back off". With language we can pass on culture. Culture is just another name for crystalised wisdom. Ten billion humans (more or less) have lived and died and left their little spit on on the accreting ball of human wisdom, just so you can have it passed to you in a couple of decades of words. For crissake have the humility to believe that this vast and magnificent work has something to teach you beyond that which you can work out for yourself.
You are being an idiot
Your friends won't tell you. In fact it will be their idea. Let's pierce our eyelids. Let's ride on the bonnet of the car. Let's dress like extras in a low-budget horror movie. Let's smoke this and see what happens. Please expand your frame of reference beyond the few dickheads you hang out with, and the few dickheads they elevate into cult heroes just because they can act in movies or play a guitar or write something anti-establishment. If the bulk of humanity thinks an idea sucks, just consider for a moment that maybe it does.
Stop thinking with your dick
The sexual overdrive of adolescence - the perpetual pole-vault - draws all the blood from your brain. For the sake of the remainder of your life when (if) the hormonal tide recedes, try to retain a little objectivity, will ya?
Choose your friends, hobbies, courses, clothes and the rest of your life for more reasons than just getting laid. Try to think and talk about something else occasionally. And just because she's willing to kiss or turn it up for you, doesn't mean you will want to see her at breakfast in ten years' time, let alone forty. Separate lust from love, and don't get her pregnant (the kid deserves better).
Tha't all you need to hear on a regular basis. Good luck.