Attempt to sleep at least seven hours a night and accept that he /she is never coming back.
Accept that the past is irreparable and dwelling on it will change nothing.
Dwell on it anyway, and then move on.
Travel—alone, if you can.
Avoid the tourist traps, learn one to ten and please and thank you in the local language, and you've already surpassed 90 percent of all the tourists who have ever been there before you.
Acquire new talents for the sake of acquiring them.
If you're young, learn an instrument if possible, you will never have this much free time ever again.
Exercise at least three times a week vigorously.
Buy clothes that fits properly, you'll notice the difference in your dating life.
Always check your system has the specs to run the game—fuck.
Always check the milk is in date—fuck.
Always check the lid hasn't fallen down—fuck!
Accept there will be whole weeks when you understand nothing and everything hurts except sometimes stupid people get lucky, and sometimes smart people never make it.
Accept that girl in class likely isn't going to strike up a conversation first, but if you do it will probably go alright.
Accept that just because it's weird, doesn't mean it's clever.
Accept that George Lucas does deserve respects regardless of the prequels.
Accept it's okay if you can't use chopsticks.
And accept that there is a set point in the future, after your death when you'll be thought about for the final time by a friend or family member and then forgotten from history forever...
Spend more time with your parents if they're alive.
Even if they are nob ends, there will come a time when they will be gone, and there will be no one to phone home to, no more hugs, no more bickering, no more in-jokes from your childhood.
Argue about politics if you must, but accept that the other person won't change their view if you start being a dick—besides even from a tactical perspective being nice is always more likely to persuade someone anyway.
Follow cutting-edge physics if you have the time.
It is the process of humans learning to speak fluent universe.
Accept that expensive whisky is almost always worth the money.
Accept that expensive running shoes that almost never worth the money.
Accept that YouTubers and online personalities are often people who couldn't get into the field they wanted to.
Do not take their word as gospel.
Especially pretentious advice from disembodied smart arse narrators, whose life is probably considerably duller than yours... mhm...
Attempt to tolerate meta humor? [1. Look out the window. 2. Look out the window some more.]
Accept that no one is in charge, not properly and no one has a handle on any of this (not even Stephen Fry).
Avoid the new season of Twin Peaks if you wish to conserve your sanity, watch it if not.
Come to terms with the fact that there is probably no absolute truth that you'll grasp in your lifetime.
However, if someone at the party tries to tell you everything is relative, invite them to exit the building from the 5th floor and see if gravity is also a social fucking construct.
Do not be intimidated by people who use long words—they are likely more insecure about their own intelligence than you are.
Instead afford them your most "effervescently magnanimous approbation."
Before tidying up, make the bed, suddenly everything will seem easier.
Visit the dentist at regular intervals.
Read Ray Bradbury.
Do not purchase cheap Sellotape.
It is about time someone stuck it to those bastards.
Embrace your own eccentricity.
What made you a freak as a kid, will likely make you an interesting adult.
Learn the names and positions of at least four constellations.
I recommend Orion, Ursa Minor, Ursa Major, and Cassiopeia.
This is guaranteed to be useful in a romantic setting at some point.
Try to eat less salt.
Try to eat more vegetables.
Try to accept that happiness isn't a constant state, nor does it come for free.
It is a chemical reward for hard work and to get more of it one has to do more... hard work.
This applies to careers, relationships, friendships, and especially Factorio™.
Diet if you want to, but acknowledge that all diets, however elaborate, are all variations on eat less, move more.
Keep a journal if you have time, it'll serve as a snapshot for how silly your life decisions are right now, and you can read it in ten years and chuckle and write some more and then you can read that in another ten years and have another chuckle.
If you're of legal age, vote for Christ's sake.
Attempt to locate your passions.
When you locate them, see if they can be monetized.
If they can, congratulations you've just discovered your career.
Prepare for crippling failure.
It is the ultimate character building, and almost no one successful has ever avoided it happening to them multiple times.
If something terrible befalls you, and you think nothing this bad has ever happened to anyone ever before, remember it has, worse, repeatedly and to almost everyone.
They got through it.
Some of them are probably going through it right now, they just haven't told you.
You will almost certainly be fine.
Stay away from synthetic weed.
Resist the appeal of depressing nihilism—if everything is pointless, you may as well just be in a good mood anyway.
Grow some kind of novelty facial hair if necessary, but don't get all uppity when no one takes you seriously.
In the words of John Waters: "If you go home with somebody and they don't have books... don't fuck them."
Spend good money on mattresses.
Don't put sugar in someone else's tea unless specifically requested to.
Do not dig down.
Ignore all of the previous instructions.... except this.
And most important and vital to happy living without parallel—floss, it is essential for good dental hygiene.