In 'six memos for the next millenium' Italo Calvino explores six principles, which can be adapted for use as flexible heuristics

• Lightness
• Quickness
• Exactitude
• Visibility
• Multiplicity
• Consistency

Full text: http://www.stanford.edu/~protass/files/Calvino_Six%20Memos%20for%20the%20Next%20Millenium.pdf Paraphrased summary: http://therumpus.net/2010/11/six-memos-for-this-millenium/