The Basics:

A B C, 1 2 3, ERRATA

At Install:

• Only install programs that you need
• Educate yourself on the use of each package

After Install:

• Remove unused daemons
• The Great SUID/SGID hunt.
• Use shadow passwords
• Use cracklib / npasswd or equivalent
• Add ssh (or equivalent)
• Customize and recompile kernel

General system hygiene and upkeep

• Backups
• Monitor the logs
• Install the Errata (mantra)