My basic advice is this:
1. Don't post intoxicated.
2. Don't post angry.
3. Don't post after midnight.
4. Don't have current students or parents as friends on personal social media profiles.
5. Everything is public and never goes away- no matter how you adjust your settings.
6. The First Amendment will not keep you from being disciplined.
Don't get me wrong- you have a right to post your personal opinions about any number of topics online. But as an education employee, if you cross the line by bad-mouthing your employer, school, parents, or students or if you're vulgar or post something that disrupts the learning environment, you're likely to be disciplined.
I have an in-depth training that I can do at your work site if you'd like to know more about this very important topic.