My rules for systems administration:

1. Openness succeeds.
2. Backups are sacred.
3. Use a versioning tool with all documentation, code, scripts, configuration, packages, everything.
4. Hard drives fail.  Plan for it.  Use RAID.
5. Automate everything.
6. Testing is a religious ritual.
7. Some things are best kept on paper.  Never be without a pen.
8. Multiply your time estimates by 4.
9. There is nothing more valuable than your own network of IT folks.
10. Use the last day of the week for documentation, coding or anything other than making changes to anything that’s remotely production.

Other General Quotes:

1. NO system should EVER rely on user behavior to remain stable
2. You either do your job well, or you do your job continuously.
3. Every time I fix a problem by rebooting (rather than knowing the real cause and fixing it) I feel a little bit of me dies inside. It hurts our industry and our profession when we develop bad habits like guessing instead of knowing. — Tom Limoncelli