Don't get married before you're 25
Around 30 years old your body stops healing, injuries are just things you live with forever now, and old injuries you thought had healed come back as forever pain.. just keep that in mind when doing stupid shit... This includes injuries to your lungs and mind from things like smoking and drugs.
If you want to help people in any way, get rich first. No one will pay you enough to live off of for helping people... Better to bring your own wealth to the table and hopefully be able to help people for real with it.
If you don't already know how, learn to code asap... In 20 years, programming will be one of the few jobs left... Maybe