same project, not all learned at the same time...
-always leave extra room for electrics to get access
-make sure that you know everything there is to know about what you're drawing/designing before you work on it
-always fill out the title block if you want them to build it... even for a cnc path
-no one ever reads the notes... not even the call-out leaders
-sometimes people are very nice and take the time to show you where you made mistakes, how they were fixed and what it cost... even if you were on a family vacation when it all happened.