What metrics should I track for conversion optimization?

Track primary conversion metrics (conversion rate, revenue per visitor, cost per acquisition), funnel metrics (drop-off rates at each stage, time to convert), engagement metrics (bounce rate, pages per session, time on site), and quality metrics (return visitor rate, customer lifetime value). Also track secondary metrics that might be affected by changes. Focus on metrics that directly relate to business goals. Avoid vanity metrics that look good but don't impact business. Example: For an e-commerce site, primary metrics might be conversion rate and average order value, while secondary metrics include add-to-cart rate and checkout abandonment rate.