Lots of good advice from others... I'll try not to repeat:
0) Regardless of what anyone says - you get one life, and one journey - and the path you take is your own - there is no right or wrong one that anyone can decide for you. It's subjective, and up to you to do what's right for you - which could be anything from being the next Ghandi to being the next Hitler.
1) No matter how much you ask this (good for you) you're still going to be the age you are and make mistakes. Mistakes are how you learn - and that's okay.
2) Don't leave everything for the future. live in the here and now, and cultivate a lifestyle that takes care of your future as well as letting you enjoy life now.
3) Avoid debt at all costs - even when all your peers, even the whole of society seems to think it's "okay" to spend money you have and pay it back later.
4) Avoid investments unless you really understand them - there is nothing fundamentally wrong with cash in the bank. (Despite all the peer pressure to invest over the years, I've been disappointed by almost every single investment I've made, and I've been quite happy at my choices to keep cash - especially when markets crash and things go bad. That cash has kept me worry-free and happy far more than any investment.) (Of course, I might be completely wrong.. but you asked.)
5) As soon as you have an income, make sure you are saving something every paycheck - build up a cushion and keep building it up indefinitely. You should very quickly not care when payday is. IT may seem like a burden at first, but it will very quickly become a source of relief and enjoyment in life - and it keeps you open to far more opportunities.
6) Happiness is something you cultivate internally and is completely up to you - it is not based on ANY external factors unless YOU let it be. Cultivate happiness in your life.
7) Drugs are bad. Some aren't as bad as the media makes things out to be when you grew up, but they're still bad compared to not doing them. (this includes drinking and even caffeine. I'm not saying don't do them - I'm just saying, after a good chunk of your life has passed, someone I met once told me he wished he hadn't done all the substances he had done, and they weren't even what you'd consider bad, and he is still relatively healthy and quite successful.)
8) Variety is good.
9) Sleep is important.
10) Food and diet and exercise are important.
11) You sort of start going downhill around 30 (You notice changes in your body and mind - you realize you aren't going to live forever. The better you take care of yourself before this point (and after of course) the better you'll feel. Health breeds happiness. Don't wreck your health early - you may not even realize you are doing it. Save some of it for when you are older and can afford to blow some more brain cells on enjoyment - otherwise you may not be able to.
12) Never feel stuck - life is full of opportunity and happiness, and the world is a beautiful place. If you wake up and find you don't see it that way, figure out why and do something about it. It's the DOING that's important.