What can you do to keep your personal life out from under the business microscope? For starters, change your privacy settings so that only friends can see your profile. Click Settings > Privacy Settings to make the necessary adjustments.
At the same time, think about how your profile makes you look from a professional perspective. Have you a joined a bunch of idiotic Facebook groups? Made lewd or inappropriate comments? If there's anything you wouldn't want an employer to see, get rid of it.
This is all pretty common-sense advice, but I suspect few Facebook users ever stopped to consider how their social-network activities would look to an employer. I sure didn't. So long, Pizza-Eaters Do It in the Oven group!