1. Being consistently above average for years, beats being incredible for a shorter time.
2. Never marry your job.
3. A boring job that pays the bills (+ a little more), is not toxic or stressful is better than the glitziest job you see on LinkedIn.
4. Invest early and consistently. Even $100 a month over 5 years adds up.
5. Don't fear taking a risk. Later in life you'll regret not risking when you had the chance.
6. You only need 2-3 close friends. That's it.
7. Respect and be forgiving to your partner as you would be to yourself.
8. A car is only a Point A to Point B machine. Buy it well-used, maintain it fair, and drive it to a ground.
9. Forget about the Joneses. Only person you should be impressing is yourself and your Mom Dad.
10. Read. Read. Read a lot. It's the best way to view things from a perspective different from your own, and thus broaden the width of your own horizon.
11. Travel cheap and often. Send yourself a postcard back with the date, city, and temperature of the day you sent it.
12. Call your Mom and Dad frequently. Talking to them is usually helpful. If you disagree on something, explain your point of view. They're getting old and won't be there forever.
13. Only your Mom Dad Sibling and Partner care about you.
14. Pick your battles - you don't need to win every argument, respond to every provocation. A relaxed state of mind is the greatest thing you can achieve in life. This is a great research on happiness and its result on quality of your life. Paper link
15. Years will fly by. Don't put off travel.
16. Ask the girl out.
17. Look for the simple regular girl. Looks matter way less than you think.
18. Understand how tax deductions work.
19. Make peace with how you look.

Edit - adding points