You never know when they'll be gone for good.
Be nice to your siblings.
They are your best link to your past and the people most likely to stick with you in the future.
Understand that friends come and go.
But with a precious few, you should hold on.
Work hard to bridge the gaps in geography and lifestyle, because the older you get, the more you need the people you know when you were young.
Live in New York City once, but leave before it makes you hard.
Live in northern California once, but leave before it makes you soft.
Travel.accept certain inalienable truths: prices will rise, politicians will philander, you too will get old and when you do, you'll fantasize that when you were young, prices were reasonable, politicians were noble and children respected their elders.