1. Right now, the default is for everyone in Facebook-land to see your posts, status updates, pictures, and etc. You probably don’t want that, so go to your settings, privacy settings, profile information, then change the “posts by me” setting to “friends only.” This will lock down that opening.
2. Your personal information, like birthdays, relationship status, political or religious affiliations, or family information may be visible with the Facebook default settings. To change this, youa re once again going to go to settings, privacy settings, profile information, and set “birthday,” “religious and political views,” and “family and relationship” to “friends only.”
3. The third concern is that much of what you post on Facebook can end up being indexed on search engines. While that might be harmless, I err on the side of it not being harmless, and choose to disallow letting that stuff out to search engines. To change this, go to settings, then choose search, and un-check the “allow” box.
You can tweak individual settings on your profile page. Most of my stuff is set to “friends only” which keeps any of that information out of the view of those I don’t know, in general. Just remember that even Facebook is not truly private, and that there is always a chance your information will get out and be available for viewing by complete strangers, so caution is still urged when you are posting in Facebook.