1. You are somewhat better looking than you think you are.
2. Teenage boys always boast about having sex, don’t do it if you don’t want the girl to find out you are talking.
People always talk.
3. Not all drugs are bad, but they are illegal. It’s okay to use some at a young age, but do your research. The ones that aren’t bad are the ones that are harmless. And you may be surprised on which ones are harmless, just Google “Is __ Harmless?.” Be more than careful of who you are doing the drugs with and where you are doing them!!
4. Your parents are sometimes wrong, but you are wrong more often. As you age you will look back and realize how many times your parents were right, and you start to have the same opinions as them. In other words you turn into a parent before you even have kids. Adults don’t all say the same things because there is a giant adult rulebook they must follow. They all know stupidity when they see it.
5. People don’t remember you by the clothes you wear, although it may torture you to wear an ugly shirt, nobody else gives a fuck.
6. The clothing and hair style that you think are cool now will make you cringe when you look at photos of yourself 10+ years from now.
7. People are not thinking about you. They are thinking about what you're thinking about them.
8. You are entering a period of chronic, low-level insanity. You will look back on your teen age years and realize this. All teenage girls are insane.
9. Social Life, Sleep, and Education. Pick two, you can never really have all 3. Never underestimate Education though. Why does everybody always nag you about education? Cause without an education you can’t get a good job, without a good job you can’t make good money, without good money you can’t do anything. Education (Temporary slavery) = Freedom for the other 80% of your life. This may be hard to understand, because right now you don't need anything, your parents pay for everything. After High school everything costs money, and you're the one paying for it all.
10. If you think your breath smells, lick your wrist, wait till it dries, then smell it. That’s what your breath smells like. Don’t freak out like everyone can smell your bad breath, majority of the time it’s just you.
11. Be proud of who you are, and don’t let other people put you down. If they do, it’s probably because they’re not feeling so good about themselves. Don’t be mean back. You’re better than that.
12. Noses never hit. Braces do not lock. Teeth sometimes hit. Lips chap, but it take a long, long time. You now know absolutely everything about the dangers of kissing.
13. It's much easier than you think to get a hickie. If you get one, you will try hard to hide it. Your parents and teachers will try equally hard to pretend they don't see it, or don't know what it is. Never flaunt your hickies, you may think it’s cool but everyone around you just thinks you look like a loser.
14. The “coolest kids” in my class are all failures now. This is a simple fact. If I had known it at the time I would have thought it a very fun fact. Now I realize it's kind of sad.
15. Pinch the skin on the back of your hand, lift it, and then release it. See how fast is disappeared? Do this to somebody who is 60+ years old and it will be more like play dough and just stay there. If you want your skin to stay like it is now for a very long time, then sun screen is your best friend.
16. Teachers don’t really hate you, they just don't think that way. The good ones will love you a little or a lot. The bad ones will have the same emotion toward you that a factory worker has toward objects flying past on an assembly line.
17. Your parents don't hate you. Your parents love you more than you can even understand now.
18. If something is illegal, there is probably a good reason why. Sit down for 10 minutes and picture the worst possible outcome before doing something. Everyone looking back at their teenage years wishes they would have done this. You learn from experience and mistakes, everyone tries to help younger people try to avoid those mistakes but they will happen. At least prepare for them.
19. The things that you think will get you into trouble probably won't get you into as much trouble as you think, but will still get you into trouble. The things that you think will get you in a lot of trouble but that you can get away with, are generally the ones underestimated.
20. The things you think might be dangerous are probably more dangerous than you think.
21. Tattoos last an extremely long time. Majority of people regret the tattoos they got as a teenager. Wait until you are 20+ before deciding.
22. Nose rings and tongue studs last only as long as you want them, but bother parents just as much.
23. You're not stuck. It will end. But it's going to take a long, long time. And once it ends you will wish it didn't.
24. If you are too nervous to buy a condom or if you think you don’t need a condom, then you are too young to have sex. Don’t double think it, it’s true.
25. Its way easier than you think to get a girl pregnant. Ever see those people with 5+ kids? Most of the time they only planned for 1 of them, some didn’t plan any of them. In fact, you were most likely an accident.
26. Life is not always a euphoric good time. You may have to battle depression, you may have financial struggles, you may have trouble finding a good partner, Many nights you may lay awake at night because you can’t shut your brain down. All of these things are normal. Don’t be afraid to ask for help in whatever way you may need it.
27. Don’t accept the bank overdraft or credit card till you’re earning twice the minimum wage.
28. The world is a big place full of amazing people, exotic places, insider knowledge, and lifetimes of stories. You don’t know it all. Neither do I. No one does. Keep that in mind. Teenagers think they know more than they really do.
29. Life after high school is nothing like life during high school.
30. You are beautiful and amazing, even if no one’s told you that - even if no one treats you that way. You have something valuable to contribute to the world, and you owe it to yourself to be; to do; to share. Everyone has the potential to impress everyone around them. Don’t abuse that power.
31. When you talk about your friends “anonymously” on Facebook, we know exactly who you're talking about, so cut that out, it's just annoying. People are smarter than you think.
32. “Follow your heart” is probably the worst advice ever. It's the perfect way to end up infatuated thinking you're in love. (Infatuation - People thinking they are in love but when indeed it is just a deep lust or like for another person. Very common.)
33. The number of times you say “I hate drama” is a pretty good indicator of how much you love drama.
34. Smoking is not cool. Majority of people find it a turn off and look down on people who smoke. Smoking is like paying to have sex with a prostitute that has every STD known to man, and being well aware that she has every STD known to man, but doing it to appear “cool” to your friends. In the end you are just paying to damage yourself and nobody really thinks it’s cool. Smoking cigarettes would be a mistake, ask anyone.
35. Acne can be removed by placing a dry (preferably damp) towel over your pillow every night and constantly cleaning your pillow casings. As well as not touching your face. If you have bad acne, wipe your face with a clean rag, towel, or paper towel whenever you get the chance. Don’t wipe your face on your shirt.
36. Knowledge is Power. That’s not a bullshit line. You may think that you’re considered “Uncool” if you read a lot of books or are the smartest kid in your class, in reality that’s total bullshit. It’s that nobody likes listening to a kid spurting out hundreds of facts or being the first to raise his hand on every question. You can be smart without doing that. I was very popular and very educated. I hung out with everyone. The losers, the preps, the stoners, the teachers, the rednecks…etc.
37. If you fear that somebody won’t be your friend because of who you are friends with, then you don’t want to be friends with them. That shows immediate unwanted traits; generally egotistical, controlling, and cocky.
38. You will never see or talk to 90% of the people in your class after High School (unless you live in a very small town).
39. If you kiss-ass to your parents, be that perfect child, and get amazing grades. They will practically let you do anything you want. It’s funny how often teenagers over-look this.
40. Be friends with your teachers! It’s unbelievably beneficial!! I’ve had teachers skip assemblies with me, I’ve been to dinner party’s with my teachers, I’ve had teachers give me grades for not doing anything, I’ve had teachers try to hook me up with their daughters or family (3 separate times), I’ve had teachers pull me out of classes I didn’t want to be in, I’ve had teachers buy me lunch, I’ve had teachers talk me out of trouble, I had teachers tell me gossip and drama about other teachers, and I even had teachers help me with my Senior prank! How did I manage to do this? I talked to my teachers as if they were peers, I asked about their life, stayed after class when it wasn’t necessary when they were in a bad mood to cheer them up. Teachers are people too, they are just older! You’re probably thinking “OMG this sounds so crazeih I don’t get it?”, that’s cause you see teachers as people you are forced to be with. Try acting like you love being around them = Easy High School life.
41. There are many things that one day as you age will just click, and you will understand. I can tell it to you now and you will think you understand, but you just won’t until it clicks. One of them is how important school is.
42. Don't lie about how many times you've had sex, it really doesn't matter.
43. If you tell something to a teenage girl, just assume she is going to tell it to another girl. She may not do it right away, but if she gets mad at you she will talk. Also girls boast about sex too.
44. Growing is natural, never spend too much money on clothes. Shoes are fine so long as you keep them clean (you can always sell them).
45. Alcohol needs to be respected just like any other substance. It's poison, so don't try to impress your friends with how much poison you can drink. There is no problem with drinking casually though. I personally don't drink.
46. Build your resume! Take part in every club and sport in your school that interest you, even if it's just for a week.
47. Just cause you have money doesn't mean you need to spend it. Saving is always a smart decision.
48. Don't be upset if a boy or girl doesn't like you back, you are not the person everyone is looking for, nobody is.
Don't blame yourself, it just wasn't a match.
49. Not everyone thinks like you. So if you think "Man green shirts look gay" Nobody is thinking that when you are wearing a green shirt except yourself.
50. You will always remember the time you lost your virginity. It’s something you don’t forget (unless you were drunk).
51. You are young, so enjoy it: Make mistakes. Work hard. Party hard. Have fun. Study. You’re probably full of energy; You won’t always be, so take advantage now.

Added:
52. Don't pursue a job, interest, or education just because it's what your parents want you to do, or because it pays out big money. You'll most likely end up realizing you hate it, or you'll spending your life trying to convince yourself you'll one day come to enjoy it.
53. Question older people constantly. Asking questions will result in answers and knowledge. They've experienced what you're experiencing, or about to experience. I've questioned older people my entire life and it would blow your mind the amazing things you'll learn. Ask the 90 year olds what they regret not doing in their life, they'll all give similar answers. What makes you think you're going to be a different story when you're 90? Life is short.
54. As you age your family starts to treat you more like an adult, use this to your advantage to learn badass stories. They won't be around for ever to tell you how much of a troublesome teenager they were.
Ask questions like; Whats the baddest thing you've ever done? Whats the funniest thing that's ever happened to you? Tell me a funny story. Tell me an embarrassing moment in your life.
Most of my memories of asking people these questions resulted in laughing till I cried. There is nothing wrong with laughter.
55. Learn to drive a stick shift as soon as possible. Some people go their entire life stuck with Automatic cars because they don't know how to drive a stick. If you can drive, set a plan with a family member or friend to do it when the weather is nice.
56. Don't drink and drive or even get into a car with a drunk driver . Shouldn't even have to add this but there are so many idiot teenagers who ignore it. I watched a person die in a car that caught on fire in front of my house. There is nothing sadder than standing on my front porch and watching their family cry and put flowers on the street light every week.
57. Think before you speak. People leave open a good 3 seconds or so for a response before questioning your delay. Use this to your advantage. In fact, nobody wants you to say the first thing that pops into your mind instantly. Unless of course it's a woman trying to manipulate you. We'll save that for another number  -Credits to Fr33zeface for this one. I just reworded his suggestion.
58. Girls will sometimes leave items at your house on "accident" as an excuse to come back another time. If you don't like a girl or you don't want her to come back, make sure she doesn't leave her shit at your house. Ask her before she leaves to check and make sure she didn't forget anything.
59. Girls flaunt their breasts because they want you to look. Don't let them play that game where they are like "Why are you looking at my tits?" Ask them why they decided to push them up and leave three buttons down.