What kind of advice to give a 15 year old boy about life?

My baby cousin is about 8 months old and my sunt asked our family to write letters to him that he could open any time in his life we choose. i want him to open mine when he is 15, just entering high school, and all that. I am 16 now,( and a girL) so i thought that i could give some pretty good advice. any ideas for what to say would be greatly appreciated!! thanks:)What kind of advice to give a 15 year old boy about life?
Tell him or her not to expect too much from ppl. Work very hard for what he or she wants. And if they need any advice they can always come to you in time of needWhat kind of advice to give a 15 year old boy about life?
tell him how life is now how a lot of people are out of work people are losing there homes left and right. Tell to stay in school and go collage and get into the medical field Tell him he has dimples just to mess with him see if he turn red as a joke
You said you could give good advice, but then you ask for ideas... what is your idea of good advice? Write that. Talk about getting good grades in school and not getting on the internet.