Backup backup backup.  
 
Also it's good to have a web editor that will color code php and smarty templates for you.  Makes reading the more complex files much easier than reading it in something that doesn't color code it.  I use HotDog by 
www.sausage.com   I've been using that software for about 10 years now.   I think there are some good free editors out there though now. 
Carrie