I've started accumulating rules of systems administration on my office wall, which I'll replicate here. 

• If it isn't documented, it does not exist. 
• Backups are a myth. Until verified. 
• Doing it manually:
  • once is research
  • twice is testing
  • ten times is dumb
• If not in CM (configuration management), it did not happen. 
• Automate it. Batch it. Remote it. 
• It might be the only way to do it, but it still will be a problem. 
• Sometimes being lazy is efficient, sometimes it's wasteful. Wisdom is knowing the difference. 
• Ask the "dumb" questions. 
• Always double check. 
• Label it! Repeatedly. On both ends!
• Few things live longer than a bad decision. 
• Always have a backout plan. Always have a way out when things go wrong. 
• Proper Planning and Preparation Prevent Pretty Poor Performance.
• Fail to plan, plan to fail. 
• Fail to test, fail the test.