Recently Facebook expanded the options available to users to better control who they allowed to see what information on their Facebook page. I encourage you to really think though what policies you enact on your page to correspond to your goals of using the site.
Are you just using Facebook to interact with your close Friends and you post very personal information? Then you may want to consider setting your privacy options high, and only allow people you've personally let into your sphere see your information and photos.
Are you using Facebook to communicate information about you, the real estate professional? Then I would recommend being more lax on your settings by allowing people you might not be connected with to see a lot more about you. For example, if a potential client types your name in a search engine, you want them to be able to learn more about you, even though you don't yet know each other.
You can also do a combination of these two. For example, people can see your Brokerage name and Profile picture, but not any photos you've uploaded.
How do you control this? Log on to Facebook. Mouse over the Setting Options in the top bar, and click into Privacy Settings then Profile Information. From there your be walked through a series of options.
As a real estate professional, which usually means you want a pretty public persona and to be highly accessable, I would recommend people are at least able to see your profile picture and some basic information about you. You just need to decide how much "Face" you want to put forward, and now Facebook allows you many more options on how to do this.
I am basically an open "Book" - with very public settings. However, I don't post anything that I don't care if everyone, including people I don't know, saw.