Rule of Modularity: Write simple parts connected by clean interface
Rule of Clarity: Clarity is better than cleverness
Rule of Composition: Design programs to be connected with other programs.
Rule of the Separation: Separate policy from mechanism; separate interfaces from engines.
Rule of Simplicity: Design for simplicity; add complexity only where you must.
Rule of Parsimony: Write a big program only when it is clear by demonstration that nothing else will do.
Rule of the transparency: Design for visibility to make inspection and debugging easier.
Rule of Robustness: Robustness is the child of transparency and simplicity.
Rule of Representation: Fold knoweledge into data, so program logic can be stupid and robust.
Rule of Least Surprise: In interface design, always do the least surprising thing.
Rule of Silence: When a program has nothing surprising to say, it should say nothing.
Rule of Repair: Repair what you can--but when you must fail, fail noisily and as soon as possible.
Rule of Economy: Programmer time is expensive; conserve it in preference to machine time.
Rule of Generation: Avoid hand-hacking; write programs to write programs when you can.
Rule of Optimization: Prototype before polishing. Get it working before you optimize it.
Rule of Diversity: Distrust all claims for "one true way".
Rule of Extensibility: Design for the future, because it will be here sooner than you think.
All these rules are from the book:
The art of UNIX Programming, written by Eric S. Raymond.