Keep Subjects Short: Email clients truncate long subjects; keep under 50 characters Use Dynamic Placeholders: Always include {invoice_number} and {amount_due} for clarity Bold Important Info: Use <strong> tags to highlight amounts and dates Include Payment Link: Always add {payment_link} for easy customer action Progressive Tone: First reminder friendly, second urgent, third final reminder Avoid Spam Triggers: Don't use ALL CAPS, excessive punctuation, or spam words Mobile Friendly: Keep emails simple; default wrapping handles most layouts Test First: Send manual test reminders using the Payment Reminder button on dashboard Use Business Hours: Send times during business hours (8 AM - 5 PM) for better open rates Consider Time Zones: If global customers, remember WordPress uses one time zone