addslahes and magic quote woes

I am trying to make my PHP safe against malicious data user inputs. Reading up on this most people suggest using addslashes(), magic_quotes on and other things like mysql_escape_string(); But I have been running into the problem that I mess up the user's input because I use more then one of these functions in succession on the data. Is there any way to prevent the "re-escaping"/"re-slashing" of data that has already been escaped or slashed? Jc