Don’t open files you don’t recognize or from people you don’t know and trust.
Don’t open files attached to chain letters, even if they come from friends.
Once something is on the internet you can no longer control who sees it. Don’t post anything you wouldn’t want the world to see.
Be suspicious of sites that ask for your home address.
Keep the computer in a common area of the house, not in a child’s bedroom, so parents can monitor all computer activity as it occurs.