Get to know the social media sites that your kids are using. Set up an account, cruise around the site, and educate yourself on what each offers and how kids are using it. Be familiar with sites' age restrictions and know that kids can easily get around them. If you have a child under the age of 13, check the browser history on your computer. If you see Facebook listed, assume your child has created an account. Talk to her about why the age requirement exists and how it might be a good idea to hold off on joining.
Consider having access to any accounts your child has set up in her name. Or, set up an account and insist your child become your "friend" or a part of your network. This will allow you to be aware of any inappropriate behavior that might be going on, and it will also act as a reminder to your child of the transparency of this virtual world. Print this parent/child online agreement form so you can both agree to the rules and know what is expected ahead of time.
The Kaiser Family Foundation recommends children between the ages of 8-18 should not use technology (computers, television, smart phones) for more than three hours a day. Set time limits to avoid technology overload, and to ensure your child isn't neglecting other areas of his life (like homework). Also, limit technology use to common areas of your house.
Remind your child that once something goes on the Internet, it can stay there forever. Common Sense Media offers a good tip: if it's something you wouldn't want posted on the hallways at school, don't post it online or send it in a text. This includes anything involving drugs, alcohol, nudity, and sexting.
Also, talk to him about how his online behavior can affect him down the line. Colleges, and even some employers, often surf social media sites when researching candidates, so warn him against posting anything that could potentially be embarrassing or harmful. As we all know, kids can't always foresee the kinds of behaviors they'll regret down the line.
Set your child's privacy settings so that only trusted friends and family can see any activity. Don't allow your child's location to be posted, and warn her about the safety implications that posting (or "checking in") where she is might pose.