How do I analyze my GRE errors effectively? (error log / granular analysis)

Log every wrong answer and categorize it at an actionable level. "Careless" is not actionable. "I misread the question," "I miscopied my own handwriting," or "I answered a slightly different question than what was asked" are actionable because you can build a specific habit to prevent each one. The right level of error logging is the level at which you can actually do something about it.