Hey, where did my drawing go?  Or worse yet, why won't AutoCAD open my drawing?  Invalid file format?  Oh, oh, where is that network backup?

These are the dark questions that may arise, hopefully rarely, when you have a problem drawing.  ALWAYS, ALWAYS have the "create backup copy with each save" checked in the Options dialogue box under the Open and Save tab.  This incredibly important setting will create a copy of your drawing, when you use the Save command, and rename the extension of the new file to .bak.  That means you simply rename the file with a .dwg extension and you have a good drawing! 
Some users prefer to leave the automatic save feature on but, this tends to make people get lazy about saving the file.  I have thousands of hours of drawing time under my belt and have never used the automatic backup file EVER.  The times where a file got corrupted, I would just rename the .bak file.  Problem solved! 
The saved .bak files are created in the current directory and should only be deleted if you are performing a master archiving of the project.   My rule of thumb is to use the Save command after every five to ten commands.  Taking a break, use the Save command.  Stopping for a phone call, use the Save command.  The time it takes to save a file is nothing compared to the time it takes to create the file from scratch!  This rule applies to all software!  Word, Excel, whatever you're using

Some habits, like using the save command, are invaluable for life lessons learned.

Save often!