They should set aside a weekly amount to a savings account (an automatic deposit) or if their job offers a 401k do that. They should also invest a small amount into the stock market (acorns is good for this if you don't know what you're doing) and keep adding to it. That's my savings advice.

They should open a credit card if they don't already have one (length of credit history is important for good credit) and don't buy anything you can't immediately afford. I recommend buying your monthly train pass or any other monthly expense with your card. Then when the bill comes immediately pay it in full. Don't ever pay the minimum because you'll accumulate interest. Your credit score will slowly keep rising as long as you're never late. That's my credit score advice.

They should make exercise a habit early on. Should be the first thing before eating breakfast IMO. Get up earlier to make the time for it. A good workout will benefit not only your body but also your mind. You'll have more energy, you'll be more optimistic, you'll sleep better. You'll pay less medical bills when your body isn't as spry anymore in your 30s and 40s. That's my health advice.

Lastly, they should know that life is anything but fair. You have to condition yourself to roll with the punches. Last week, I fell down some stairs in my building. I hurt my left elbow and hip. Thankfully nothing is broken. I didn't let it ruin my day. These things happen, next time I may get a fracture. What's important is that I can get up and go about my day like nothing happened. I have more good days than bad days. People tend to remember bad days more vividly. You should have a stoic mindset. We can't worry about things we can't control. That's my life advice.