Go to Facebook and find your own profile. Under account, hit privacy settings.
At the top it says "basic directory information", some text, and a tiny link that says "view settings". Click that link. The first 2 are fine to have be everyone: search for me and send me friend requests. The rest, if you'd like to be more private, could either be friends and networks, friends of friends, or friends only. "Networks" means, if you say you went to a college, anyone from that college can see it.
When you're done there, click "back to privacy" at the top.
Under "sharing on facebook", click "custom" and find the little blue "customize settings" link. For each piece of info you have, you can choose who can see it. I have "friends only" for most of it but i let "friends and networks" see some things and for my website URL, which is how I advertise my services, it is set to "everyone".