How to Change Your Account to Private on Facebook
Exposing all of your information on Facebook means that any of the millions of users on the site can see what you post. Your interests, wall posts and birthday are all available for browsing by the Facebook community. Protect your privacy by changing the settings for your profile. By limiting the viewing permissions for your profile, only your confirmed friends can see and comment on your Facebook page.
Click on the "Account" link located at the top of your Facebook page. Select "Privacy Settings" from the menu that drops down.
Make your entire profile hidden to everyone but your confirmed friends by clicking the "Friends Only" tab in the "Sharing on Facebook" section.
Click on "Customize Settings" to edit your privacy settings by profile section. Make a particular section of your profile, such as "Bio and favorite quotations" or "Interested in" private by clicking on the gray icon to the right of it and selecting "Friends Only" from the menu.
Return to the "Privacy Settings" menu by clicking "Back to Privacy" to edit the settings for your basic information such as current city and education. Click on the "View Settings" link at the top of the page. Use the gray icon to the right of a profile section to select "Friends Only" as the privacy setting.