Act as a seasoned email marketing specialist with 10+ years of experience in the cleaning industry. Craft a detailed guide on best practices for email marketing tailored specifically for [RESIDENTIAL/CLEANING/COMMERCIAL] cleaning businesses. Include strategies for [SUBJECT LINE OPTIMIZATION], [SEGMENTING YOUR AUDIENCE], and [CALL-TO-ACTION PLACEMENT]. Provide actionable tips on how to [INCREASE OPEN RATES] by personalizing content based on [CUSTOMER BEHAVIOR/PREFERENCES]. Also, address common pitfalls like [OVERWHELMING FREQUENCY] or [GENERIC MESSAGING] and how to avoid them. Use real-world examples and data-driven insights to support your recommendations.