You know how some applications show tips for new users in a popup dialog box on startup? Or at least, used to - it's not so popular any more.
Stack Overflow should do that. Not necessarily in a popup - that would probably just get closed without being read. But in a visible place.
Things like "It is better to show too much code than too little."
Or "State your actual problem, not just the approach you think you need to take to solve it"
Or "Did you know that questions on professional server administration belong on Server Fault, not here?"
Or "Did you know? A stack trace can be very useful to debug your Stack Overflow problems - especially if they are literally stack overflows"