Normally, facebook is used for a social interaction purpose. The information we pass on is the public information about us. your name, age, email id, address etc. If you donot want to share some information then do not.
If you wish to interact with some group of persons you know, then make them friends. set your settings not to receive any communication from others and do not send info to others.
if u are at home. there is not problem of safety. But if u use a common public computer and u r afraid of others using ur account etc., make sure u delete history in the web browser. then it is okay.
what ever it is, face book is for exchanging social public info about your friends and yourself - among you. so there is no problem as long as u stick to that.
DO NOT visit junk pages , do not trust messages or news from other users..