Appreciate the time you spend with your parents. You won't have them in your life forever.
Be nice to your siblings. Once your parents are gone, they are the only ones who have shared experiences of your childhood and remember what you were like as a child. What your early dreams were.
Marry for love and if you fall out of love then move on, you really won't fall back in love with same person.
Spend time having fun with your children. Make sure you are in their happy childhood memories once they grow up.
Understand some things are just way beyond your control and don't lose sleep over them. Focus on stuff you can control and improve.
Sort a pension on first day of work. Keep paying into it even if money is tight.
Value your health and try to fit sensible eating and excercise into your week.
Reach out to others emotionally, family, friends, colleagues. We all need others to thrive. No one wants to end up old and alone.
Learn to budget and live within your means. Don't run up debts.
Don't spend endless additional hours at work. When you are old no one looks back and wishes they had spent more time at work.
Work at your marriage, don't take your spouse for granted.