Generate a full detail guide on Conversion Rate Optimization (CRO) for websites. The guide must be a step-by-step process. It should include detailed sections on: 1. Foundational Principles: Understanding user psychology and friction. 2. Data Collection: A guide to using tools like heatmaps, session recordings, and analytics. 3. Forming a Hypothesis: A template for creating a strong, testable hypothesis. 4. A beginner's guide to setting up and running A/B tests. 5. A list of common, high-impact elements to test on a landing page. Please include a disclaimer that CRO is an iterative process.