Some have already been mentioned, but worth repeating:
1) Whatever it is you love most -- figure out a way to make your living from it.
2) Have friends of good character.
3) Pursue your dreams, no matter how grand.
4) Know now that you'll make mistakes. Try to avoid them, but don't let them get you down.
5) Don't ever let negative people hurt you. Don't let their cynicism and cruelty damage your spirit or your dreams. Ignore them -- then avoid them.
6) Stay healthy. Lift weights and do cardio your whole life. Wear sunscreen. Eat oatmeal. Don't smoke, drink or use drugs.
7) Always remember the conventional wisdom is often wrong. Question everything.
Don't be afraid to question the existence of God. Even if the process is painful.
9) Learn to think critically. Be skeptical (not cynical -- there's a huge difference).
10) Visit the bookstore frequently and read a lot. Read the newspaper.
11) Compliment others and look for ways to be kind. At the same time, always stick up for yourself and don't let people take advantage of you.
12) Remember that evil exists, in part, because otherwise good people let it happen. Do your duty.
One more thought: Albert Einstein once said "the most important decision you'll ever make is deciding if you live in a friendly universe, or an unfriendly universe."
I recommend friendly. More importantly, I think he did too.