Other rules and notes

Always split mechanisms and policies
Examples: X11, IPV4
Silence is golden
Don't make your output dirty with unneeded information
Always (always) check error conditions
It will save you hours or days of grief
Code repetition is __BAD__
Never use cut-and-paste as a programming technique
You'll replicate your bugs, and will make them unfixable
The design of your code will be hidden
Use tables and data structures to avoid repetition

http://en.wikipedia.org/wiki/Unix_philosophy

The three virtues of the programmer, according to Larry Wall
Laziness, impatience, hubris.