Key metrics that should guide your adjustments include: - Open Rates: A low open rate may suggest subject lines need improvement. - Click-Through Rates: If your click-through rates are falling, the content or call-to-action might need changes. - Conversion Rates: Low conversion rates could indicate that your landing pages or offers are not compelling enough. - Unsubscribe Rates: High unsubscribe rates may suggest that your content is no longer relevant to your audience.