I would tell my 18yo self, who would be living in 1977, to first of all,
Live poor by choice NOW, save and invest all that money you are making instead of blowing it on babes, booze, drugs, clothes, cars, and good times. All the money you are blowing could grow to significant wealth by the time you are 60. Which is how old you will be when you are me, talking to you, which I am doing now and you will be doing 42 years from now.
When they invent mutual funds, go in big. Meanwhile invest in stocks stocks stocks. Mix it up. Mega cap, mid, small cap. Buy and hold until you have time to learn how to trade.
Another thing you will hear about in a few years are IRAs and especially 401Ks. The tax breaks will give you a huge advantage. NO MATTER WHAT, always put the max in there, every year, no excuses, at least for the first 30 years. The first ten years will matter the most.
No, you don't have your whole life ahead of you. You don't have plenty of time to get your shit together. Do it NOW, or feel the pain later. Yes, you are going to live past 40. In fact, you will probably live past 80, and you will want to have some money to make being an old guy a cool thing instead of a real drag.
Don't invest in BetaMax or 8 track. In fact, give vinyl a miss too. Ditto Laser Disc. When a company called Blockbuster Video comes out, buy and hold, but sell as soon as you start hearing about a thing called streaming video.
Pay your income taxes. Some bitch will rat you out in 1985 if you don't. You aren't working off the books. You just THINK you are.
Invest in Amazon and Facebook and Google and other crazy sounding dot com stuff. It will all go tits up for a while but you can sell the first time you see across the board declines, and wait it out.
Your first marriage will really suck. But that's okay cause it will save you from marrying ************** *******. Trust me, she would be the worser of two evils.
In a few years you will have a kid who will grow up just like you except he will be lazier and even more irresponsible. Get over it.
The 63 Chevy truck? Don't sell it. In fact, get a half dozen more while they are cheap. You are really gonna miss that truck some day. Just for fun, stick a 350 from a wrecked corvette in one of them. You can do the swap in a day with only a couple of very minor changes. Put a few sacks of sand in the bed for weight and it will run like a whipped monkey. Oh, in a few years you will pick up a Nova, same year and put a v8 in it, too. Don't let the bitch drive it, ever. Don't ask what bitch... you will know who I am talking about when the time comes.
The Saints will win the Super Bowl in 2010 so bet bank, boat, and baby on it.
Get a computer. Every year, get the latest and greatest. Learn to program. Don't get too wild about Visual this and Visual that, when it comes out. It will be too limiting. In 1991 an operating system called Linux will create a lot of opportunity to use a programming language called ANSI C and later, C++. Learn that. Give Assembly a miss. Learn BASIC in its various iterations because later on a language called PYTHON will bear a striking resemblance and will be very useful. When online stock trading becomes a thing, jump in with both feet while the money is still easy.
I was gonna tell you about Bruce Jenner but I will just let that be a surprise.