(Much of the information in this post comes from my computer savvy husband.)
So many of us have Facebook or Twitter accounts. We have LinkedIn profiles and so forth. We can use social media to our benefit or to our detriment. Many of us love to share our thoughts and pictures with others.
In general, consider what you post as available to the entire world. Avoid putting personal information such as birth dates, addresses, certain photos, and your daily habits. People can use this information to steal your identity, stalk you, or break into your home. Victims of abuse should use more caution since abusers can find them more easily through social media. You have to weigh your options.
Facebook has some advantages and disadvantages. You can adjust your privacy settings, but that isn't full-proof. You can block people from seeing your wall. Facebook does not respect your privacy when it comes to sharing information with government entities. Police have full access in the United States to your wall and any private messages you send. Most police and politicians are fine, but not all. Some police and politicians use this as a way to exact revenge and stalk others. Also, abusers who work for law enforcement have access to their victims' accounts.
I don't know as much about Twitter, but I do know more about their privacy record dealing with the government. Twitter will not reveal your messages to any government entity unless a court orders it. Even then, Twitter will fight for your privacy.
LinkedIn is unreliable. It does little to protect your information and password. So if you use LinkedIn, use a different password from all of your other accounts.
Recently, someone found a flaw in internet security where it's possible for hackers to easily get your password. This flaw has been fixed on many websites, but you should change all your passwords anyway. You can't be sure any hacker hasn't already stolen your password before the flaw was found.