Squeaky stuff

The door to my deck has been squeaking for a long time and it's getting worse. What should I do to fix it? I was thinking of getting a can of WD40 but I have a vague recollection that somebody once told me that it's bad to use it for doors. So what do I need? An oilcan like the Tin Man has in the Wizard of Oz? I haven't seen one of those in many years.